Newton’s Laws of Motion: a full term of science

Ten ready-to-teach lessons for Year 10 Physical sciences. Print this pack and the term is prepared: every lesson comes with a step-by-step plan, the questions to ask, a student worksheet, cut-out cards, a class sheet or exit tickets, an assessment kit and worked answers.

Start here: five minutes to Monday

1. Skim the term at a glance on the next page.
2. Print the lesson you need. Each lesson is three A4 sheets: plan, worksheet, and cards, a class sheet or tickets.
3. Gather the few items under “You need” on the plan. Most come from the classroom or the science prep room.
4. Open the free interactive unit on your board or projector. Every plan tells you which picture to show and when.
5. Teach straight from the plan. Timings, talk prompts, misconceptions and worked answers are all on the one page.

For any Year 10 science teacher

The pack suits a physics specialist and a teacher working outside their own subject alike: each plan explains the idea in plain words, lists the misconceptions students bring, and gives worked answers. The big idea of the term: forces change motion. With no net force an object keeps doing what it was doing; a net force makes it accelerate, by an amount set by a = F ÷ m; and forces come in pairs, equal and opposite, acting on two different objects. Students investigate each law with trolleys, balloons and spring balances, measure the relationship between force, mass and acceleration, and use it to explain weight, falling and road safety.

Two ways to run each lesson

Every lesson works as one 60-minute block, or as two 30-minute sessions; the split point is marked in every plan. Look ahead: Lessons 4 and 5 need a trolley, a pulley clamped to the bench and a set of slotted masses for each group, and Lesson 9 needs a raw egg in a zip-lock bag for each group.

Safety and care in one look

Keep feet clear of hanging masses and put a box of sand or a cushion under them. Stop trolleys at the end of the bench with a buffer. Balloons are latex-free. In Lesson 9 the eggs stay sealed in zip-lock bags, students with an egg allergy take another role, and everyone washes their hands afterwards. Film only with devices the school allows.

The term at a glance

One lesson a week for a term. Each lesson stands on the ones before it, so run them in order where you can.

How the sequence builds

Lesson 1 adds forces into a net force, and Lesson 2 meets the first law. Lesson 3 measures motion, so that Lessons 4 and 5 can investigate the second law, changing first the force and then the mass, and Lesson 6 puts F = m a to work. Lesson 7 meets the third law. Lessons 8 and 9 apply all three to falling and to car safety, and Lesson 10 brings it together.

Curriculum links (Australian Curriculum V9)

The whole term teaches the Science Understanding descriptor AC9S10U05 quoted on the cover. The lessons also work these Science Inquiry and Human Endeavour descriptors:

Assessment in this pack

• Every plan ends with “Answers and look-fors”: what meeting the idea sounds like in a Year 10 voice, with working.
• The assessment sheet near the front has a class observation checklist and a three-level rubric.
• Lesson 10 is the summative pair: the lift task, plus the “Show what we know” check.

Materials for the whole term

One gathering session covers all ten lessons, and most of it is already in the science prep room. Two things are worth doing ahead: check that every group can have a trolley, a pulley and slotted masses for Lessons 4 and 5, and tie a long string across the room for the balloon rockets in Lesson 7.

The one-trip list

• From the prep room: trolleys, pulleys, clamps, slotted masses, spring balances, timers or light gates, metre rulers.
• From the classroom: cards, coins, plastic cups, paper, string, straws, tape and calculators.
• From the supermarket: latex-free balloons, a dozen eggs and zip-lock bags.

Safety and care in one look

• Keep feet clear of hanging masses; put a box of sand or a cushion below; stop trolleys with a buffer.
• Balloons are latex-free. Eggs stay sealed in zip-lock bags; students with an egg allergy take another role; everyone washes their hands.
• Film only with devices the school allows, and only the equipment.

Assessment without extra work

The term assesses itself. Every lesson plan ends with worked answers and look-fors, and Lesson 10 is the summative pair: the lift task, in which students explain why bathroom scales read more or less in a moving lift using all three laws, and the final check. This sheet is the place to note what you see along the way.

The three levels

Class observation checklist

A tick a lesson is plenty; the Lesson 10 task and check fill the gaps.

Word wall cards

Cut out the cards and build the wall as the words arrive: force, net force, balanced forces and friction in Lesson 1; inertia in Lesson 2; speed, velocity and acceleration in Lesson 3; mass, newton, F = m a and gradient in Lessons 4 and 5; action and reaction in Lesson 7; weight, gravitational field strength, air resistance and terminal velocity in Lesson 8; crumple zone in Lesson 9.

Dear families

This term in science, Year 10 studies Newton’s three laws of motion: why things keep moving or stay still, how force, mass and acceleration are linked by F = m a, and why every push pushes back.

Along the way your student will flick a card from under a coin, pull a trolley with hanging masses and graph the results, launch a balloon rocket along a string, weigh a mass on the Moon and Mars (on paper), and design packaging to protect an egg in a crash.

Try this at home

• In a car or bus that brakes, notice which way your body moves. Why does a seatbelt matter?
• Push a full and an empty shopping trolley the same way. Which speeds up more, and why?
• Stand on a skateboard and throw a ball forwards (carefully, outside). Which way do you move?
• Ask what your weight would be on the Moon, where gravity is about one sixth as strong.

What to ask your scientist

• What does F = m a mean, and how did you test it?
• Why does a car keep moving after the engine stops pushing?
• If every push pushes back, how does anything ever move?
• Why do cars have crumple zones?

A small note on safety: practical work this term uses trolleys, hanging masses, balloons and eggs. Students learn to keep clear of hanging masses; the balloons are latex-free; and the eggs stay sealed in bags. Please let us know about an egg or latex allergy.

Warm regards,

The Year 10 science team

Printed from the free seegongsik Newton’s Laws of Motion teaching pack · seegongsik.com/au/y10/physical/AC9S10U05/pack

Net force

A force is a push or a pull, measured in newtons (N). Most objects have several forces on them at once, so what matters is the net force: all the forces added together, taking direction into account. If the forces balance, the net force is zero and the motion does not change: the object stays still or keeps the same speed in a straight line. If they do not balance, the object speeds up, slows down or changes direction. Students add up the forces in four diagrams, then sort twelve everyday situations by their net force.

We are learning to

• add forces in a line to find the net force,
• predict how an object moves from its net force,
• tell balanced forces from no forces at all.

Success criteria

• I can find the size and direction of the net force from a force diagram.
• I can explain why a car cruising at a steady speed has balanced forces on it.

You need

• the motion cards (third sheet), one set per pair, with scissors,
• the worksheet (next sheet), one per student.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the rope, the board and Part A in Session A, and Parts B and C in Session B.

Watch for these ideas

• “A moving object must have a force pushing it along.” With no net force it keeps moving; a force is needed only to change the motion.
• “Balanced forces mean the object is still.” It may be still, or moving steadily in a straight line.
• “Turning at a steady speed needs no force.” Changing direction is a change in motion, so it needs a net force.

Make it easier, make it bigger

• Easier: add the forces in the first diagram together, writing forwards as positive and backwards as negative.
• Bigger: draw a force diagram for a book being pushed across a desk at a steady speed, with all four forces, up, down, forwards and back.

Answers and look-fors

• Part A: a box pushed across the floor: 0 N, so it stays still or keeps a steady speed; a car on a straight road: 500 N forwards, so it speeds up; a skydiver (up is positive): 0 N, so it falls at a steady speed; a cyclist braking: 150 N backwards, so it slows down.
• Part B: no net force C, F, I, J, L; net force in the direction of motion A, B, E, G; net force against or across the motion D, H, K.
• Part C: 1. The drive force forwards balances the drag and friction backwards, so the net force is zero. 2. No: the weight and the upward push of the desk act on it and balance. 3. Its direction keeps changing, which needs a net force towards the centre of the turn.
• Bigger: push forwards balanced by friction backwards; weight down balanced by the desk’s push up.

Net force

A. Four force diagrams

For each, give the net force (size and direction) and say what the object does.

B. Sort the motion cards

C. Questions

What is the net force?

Cut out the three headings and the twelve cards. Sort each situation under the net force acting on the moving thing.

Teacher note: the answer letters are in the plan. The three piles are different sizes.

Inertia

Newton’s first law: an object stays at rest, or keeps moving at the same speed in a straight line, unless a net force acts on it. The tendency to keep doing what it was doing is called inertia, and the more mass an object has, the more inertia it has. On Earth, friction and air resistance usually slow moving things, which is why it feels as if motion needs a constant push; in space, a probe with its engines off keeps moving for decades. Students see inertia in three quick demonstrations, then use it to explain seatbelts and headrests.

We are learning to

• state Newton’s first law and explain inertia,
• use the first law to explain everyday events,
• explain how seatbelts and headrests protect passengers.

Success criteria

• I can explain each demonstration using inertia.
• I can explain why a passenger moves forwards when a car stops suddenly.

You need

• for each group: a playing card, a coin, a plastic cup, a strip of smooth paper, a small bottle of water, a trolley, a small toy and a book,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the bus, the board and the demonstrations in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “The passengers are thrown forwards.” Nothing pushes them forwards; the bus slows and they keep going.
• “Moving things naturally slow down and stop.” They slow because of friction and air resistance, which are forces.
• “Inertia is a force.” It is a property of mass, the resistance to a change in motion.

Make it easier, make it bigger

• Easier: do each demonstration at the front first, and agree on the explanation together.
• Bigger: explain why a bowl full of soup is harder to start and stop moving than an empty bowl, using the word mass.

Answers and look-fors

• Part A: the coin drops into the cup: the card was pulled away too quickly for friction to move the coin much, and with no sideways net force it stayed put. A slow pull lets friction drag the bottle along; a quick yank is over before friction can move it much. The toy keeps moving forwards when the trolley stops, because nothing stops it.
• Part B: 1. The car stops, but the passenger keeps moving forwards until the seatbelt pulls back on them. 2. When a car is hit from behind it is pushed forwards; the head, resting, stays where it is until the headrest pushes it forwards with the body.
• Part C: 1. More mass, more inertia: the same force changes its motion less. 2. In space there is almost no friction or air to slow it, so no net force acts. 3. If the ute stops or turns, the load keeps going and can slide off.
• Exit ticket: 1. An object keeps still or keeps moving steadily unless a net force acts. 2. Its mass. 3. The passenger keeps moving forwards.
• Bigger: the full bowl has more mass, so the same force gives less acceleration, starting and stopping.

Inertia

A. Three demonstrations

B. Seatbelts and headrests

C. Questions

Exit tickets

Measuring motion

To test Newton’s laws, we need to measure motion. Speed is the distance travelled each second, in metres per second (m/s); velocity is speed in a given direction. Acceleration is how much the velocity changes each second: a = change in velocity ÷ time taken, in metres per second per second (m/s²). Students film a trolley rolling down a ramp next to a ruler and read its position every 0.2 s, or use the example readings, then work out the speed in each interval and draw a speed and time graph, whose gradient is the acceleration.

We are learning to

• calculate speed from distance and time,
• calculate acceleration from a change in velocity,
• read acceleration from the gradient of a speed and time graph.

Success criteria

• I can work out the average speed in each interval from a table of positions.
• I can find the acceleration from a speed and time graph, with its units.

You need

• for each group: a ramp made from a plank on books, a trolley or a ball, a metre ruler; a tablet or phone to film, if the school allows,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the ball, the board and the filming in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “Acceleration means going fast.” It means the velocity is changing; a fast car at a steady speed has no acceleration.
• “The average speed is the speed at the end.” Over an interval the speed changes; the average sits at the middle of the interval.
• “Slowing down is not acceleration.” It is acceleration in the opposite direction to the motion.

Make it easier, make it bigger

• Easier: give the distance travelled in each interval, so students only divide by 0.2.
• Bigger: a trolley on a steeper ramp travels 0.04, 0.16 and 0.36 m by 0.2, 0.4 and 0.6 s. What is its acceleration?

Answers and look-fors

• Part A: results vary; the distance in each 0.2 s interval should grow.
• Part B: 0.1 m/s at 0.1 s, 0.3 m/s at 0.3 s, 0.5 m/s at 0.5 s, 0.7 m/s at 0.7 s, 0.9 m/s at 0.9 s; a straight line through the origin.
• Part C: 1. The speed rises by the same amount in each 0.2 s, so the acceleration is steady. 2. (0.9 − 0.1) ÷ (0.9 − 0.1) = 1 m/s². 3. The ramp’s slope: a component of the trolley’s weight acts down the ramp, more than friction.
• Exit ticket: 1. 4 m/s. 2. 2 m/s². 3. Its velocity is changing.
• Bigger: twice the distances at each time, so 2 m/s².

Measuring motion

A. Our trolley

The example readings are from a filmed trolley, read every 0.2 s.

B. Speed in each interval

Average speed = distance travelled in the interval ÷ 0.2 s. Plot it at the middle time of the interval.

C. Questions

Exit tickets

Force and acceleration

Newton’s second law says that a net force makes an object accelerate, and that the acceleration is in proportion to the force: double the force, double the acceleration. Students test the first half of that by pulling a trolley with hanging masses. To keep the mass that is accelerating the same, they move masses from the trolley to the hanger rather than adding new ones. The weight of the hanging masses is the pulling force: 10 g of hanging mass pulls with about 0.1 N. A graph of acceleration against force should be a straight line through the origin, with a gradient of 1 ÷ the total mass.

We are learning to

• plan a fair test that changes one variable and controls the others,
• graph acceleration against force and describe the relationship,
• use the gradient of a graph to find a quantity.

Success criteria

• I can explain why the masses are moved from the trolley to the hanger.
• I can show from a graph that acceleration is in proportion to force, and find the mass from the gradient.

You need

• for each group: a trolley, string, a pulley clamped to the end of the bench, a mass hanger and five 10 g masses, a stopwatch or light gates, tape to mark 1 m, a buffer at the end of the bench and a box of sand under the hanger,
• the worksheet (next sheet), one per student, and the class results sheet (third sheet), on the board or a bench.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the prediction, the board and the trolley runs in Session A, and Parts B and C in Session B.

Watch for these ideas

• “Adding masses to the hanger is enough.” That also adds mass to be accelerated; moving them keeps the total the same.
• “A force gives a speed.” A steady net force gives a steady acceleration: the speed keeps rising.
• “The line should start above zero.” Friction can shift it; tilting the bench very slightly can cancel friction.

Make it easier, make it bigger

• Easier: time the runs as a class, one group at the front, and share the times.
• Bigger: tilt the bench just enough that the trolley rolls at a steady speed with no hanging mass. Why does that make the test fairer?

Answers and look-fors

• Part A: results vary; the acceleration should roughly double as the force doubles.
• Part B: a straight line through the origin; gradient about 2 (m/s² per N), so the mass is 1 ÷ 2 ≈ 0.5 kg, close to the 0.5 kg used.
• Part C: 1. The acceleration is in proportion to the force. 2. So that only the force changes; adding masses to the hanger would also change the mass being accelerated. 3. Friction, timing by hand, and a string that is not level.
• Bigger: gravity down the slope then balances friction, so the net force is just the pull of the hanging masses.

Force and acceleration

A. Our trolley

Time the trolley over 1 m from rest. Acceleration a = 2 × distance ÷ time². Move each 10 g mass from the trolley to the hanger.

B. An example class

The total mass was kept at 0.5 kg. These are example results.

C. Questions

Class results: the gradient

Each group adds the gradient of its graph and the total mass of its trolley and masses. Does 1 ÷ gradient match the mass?

If 1 ÷ gradient is a little larger than the mass, friction is the usual reason. Why?

Mass and acceleration

The second half of the second law: with the same net force, a bigger mass accelerates less. Double the mass and the acceleration halves. Students keep the pulling force the same, a fixed hanging mass, and load the trolley with more mass each run. A graph of acceleration against mass curves down, which is hard to read. Plotting acceleration against 1 ÷ mass instead gives a straight line through the origin, with a gradient equal to the force. Together with Lesson 4 this gives a = F ÷ m, or F = m a: one newton is the force that gives one kilogram an acceleration of 1 m/s².

We are learning to

• investigate how mass affects acceleration with the force kept the same,
• turn a curved graph into a straight line by changing what is plotted,
• combine two relationships into F = m a.

Success criteria

• I can describe how acceleration changes as the mass doubles.
• I can graph acceleration against 1 ÷ mass and say what the gradient tells me.

You need

• the same set-up as Lesson 4, with extra masses to load onto the trolley; keep the hanging mass the same throughout,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the trolleys, the board and the runs in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “Heavier things need a force to keep moving.” They need more force to change their motion, not to keep it.
• “Acceleration falls by the same amount for each extra kilogram.” It falls in proportion to 1 ÷ mass, so less each time.
• “A curved graph means no pattern.” Plotting against 1 ÷ mass shows the pattern as a straight line.

Make it easier, make it bigger

• Easier: give the 1 ÷ mass row worked out for the example class.
• Bigger: show that the gradient of a against 1 ÷ m is the force, using a = F ÷ m.

Answers and look-fors

• Part A: results vary; doubling the mass should roughly halve the acceleration.
• Part B: 1 ÷ mass = 2, 1.33, 1, 0.8, 0.67; a straight line through the origin with a gradient of about 0.5 N, matching the 0.5 N force.
• Part C: 1. As the mass goes up, the acceleration goes down; doubling the mass halves it. 2. The graph of a against 1 ÷ m is a straight line through the origin, so a is in proportion to 1 ÷ m. 3. a = F ÷ m, so F = m a.
• Exit ticket: 1. It halves. 2. Its gradient is the force. 3. 2 m/s².
• Bigger: a = F × (1 ÷ m), the form of y = gradient × x, so the gradient is F.

Mass and acceleration

A. Our trolley

Keep the hanging mass the same. Add mass to the trolley each time. a = 2 × distance ÷ time².

B. An example class

The pulling force was kept at 0.5 N. These are example results. Work out 1 ÷ mass, then plot acceleration against it.

C. Questions

Exit tickets

Using F = m a

Newton’s second law, F = m a, lets us calculate any one of force, mass and acceleration from the other two, as long as F is the net force. Real problems usually have more than one force, so the first step is always the net force: forwards forces minus backwards forces. Students work through a worked example, four one-step problems, a car with a drive force and friction, and a crate where the friction is the unknown. Units matter: newtons, kilograms and metres per second squared.

We are learning to

• rearrange F = m a to find any of the three quantities,
• find the net force first when more than one force acts,
• show working with units at every step.

Success criteria

• I can solve one-step problems for force, mass or acceleration, with units.
• I can solve a problem with two forces by finding the net force first.

You need

• the worksheet (next sheet), one per student; calculators,
• the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the rearranging, the board and Part B in Session A, and Part C and the ticket in Session B.

Watch for these ideas

• “Use the biggest force in F = m a.” F is the net force: all the forces added, with directions.
• “Mass is measured in newtons.” Mass is in kilograms; force, including weight, is in newtons.
• “A big acceleration means a big speed.” The cricket ball’s acceleration lasts only a few thousandths of a second.

Make it easier, make it bigger

• Easier: give the rearranged form for each problem: F = m a, a = F ÷ m or m = F ÷ a.
• Bigger: the crate’s push stops. How quickly does friction slow it, and how long until it stops from 3 m/s?

Answers and look-fors

• Part B: 1. 2 400 N; 2. 1.5 m/s²; 3. 5 kg; 4. 2 000 m/s².
• Part C: 1. Net force = 3 000 − 1 200 = 1 800 N forwards; a = 1 800 ÷ 1 500 = 1.2 m/s². 2. Net force = 50 × 1.5 = 75 N; friction = 200 − 75 = 125 N.
• Exit ticket: 1. 3000 N. 2. 0.5 m/s². 3. Net force = 50 − 20 = 30 N, so a = 30 ÷ 10 = 3 m/s².
• Bigger: with only friction, a = 125 ÷ 50 = 2.5 m/s² backwards; it stops in 3 ÷ 2.5 ≈ 1.2 s.

Using F = m a

A. A worked example

B. One step

C. Two forces

Exit tickets

Every push pushes back

Newton’s third law: when one object pushes or pulls on another, the second pushes or pulls back on the first with a force of the same size in the opposite direction. The two forces of a pair act on different objects, so they never cancel each other out. That is how anything moves at all: you push back on the ground and the ground pushes you forwards; a rocket pushes gas down and the gas pushes the rocket up. Students launch a balloon rocket along a string, then match six pairs of forces.

We are learning to

• state Newton’s third law,
• identify the two forces of a pair and the objects they act on,
• explain why the two forces of a pair do not cancel out.

Success criteria

• I can name both forces of a pair, with the object each one acts on.
• I can explain how a balloon rocket moves using the third law.

You need

• for each group: a latex-free balloon, a drinking straw, tape, and about 4 m of string tied tight across the room through the straw,
• the pair cards (third sheet), one set per pair, with scissors; the worksheet (next sheet), one per student.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the wall, the board and the rockets in Session A, and Parts B and C in Session B.

Watch for these ideas

• “The pair of forces cancels out.” They act on different objects; only forces on the same object can cancel.
• “The bigger object pushes harder.” Both forces are always equal; the smaller mass accelerates more.
• “Weight and the support force are a third law pair.” Both act on the same object; the pair of weight is the object pulling Earth.

Make it easier, make it bigger

• Easier: for each card, ask first “who pushes?” and “who is pushed?”, then swap them to find the partner.
• Bigger: Earth pulls an apple down with the same force as the apple pulls Earth up. Why does the apple move and Earth hardly at all?

Answers and look-fors

• Part A: results vary; a fuller balloon pushes out more air for longer and goes further.
• Part B: G with A, D with J, E with L, B with H, K with F, I with C.
• Part C: 1. The balloon pushes air backwards out of its neck; the air pushes the balloon forwards. 2. They act on different objects, the balloon and the air, so they cannot cancel. 3. You push backwards on the ground and the ground pushes you forwards; on ice there is too little friction to push against.
• Bigger: the forces are equal, but Earth’s mass is enormous, so a = F ÷ m is tiny for Earth and large for the apple.

Every push pushes back

A. Balloon rockets

Tape the balloon under the straw on the string, keeping its neck pinched. Let go and measure how far it travels.

B. Match the pairs

Pair each card with the other force of its pair. Write the pairs of letters.

C. Questions

Pairs of forces

Cut out the twelve cards. Each describes one force; its partner is the other force of the pair. Match each pair.

Teacher note: the pairs are in the plan. Every card has exactly one partner.

Weight and falling

Weight is the force of gravity on an object: W = m g, where g is the gravitational field strength, about 9.8 N for every kilogram on Earth. Mass stays the same everywhere; weight changes from world to world. A falling object speeds up because its weight is an unbalanced force, but as it speeds up the air resistance on it grows. When the two balance, the net force is zero and it falls at a steady speed, its terminal velocity: about 200 km/h for a skydiver falling flat, and about 20 km/h with an open parachute. Students weigh masses with spring balances, work out weights on four worlds, and follow a skydiver through four stages.

We are learning to

• tell mass from weight and calculate weight with W = m g,
• explain the forces on a falling object at each stage,
• explain terminal velocity using balanced forces.

Success criteria

• I can calculate a weight on another world and explain why the mass stays the same.
• I can draw and explain the forces on a skydiver at each of four stages.

You need

• spring balances that read in newtons, and 100 g and 1 kg masses,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the question, the board and Part A in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “Mass and weight are the same.” Mass is the amount of matter in kilograms; weight is a force in newtons.
• “Heavier things fall faster.” Without air, everything falls with the same acceleration; air resistance makes the difference.
• “At terminal velocity there is no force.” Weight and air resistance are both large, and balanced.

Make it easier, make it bigger

• Easier: give the skydiver’s forces as arrows to label, rather than to draw.
• Bigger: on the Moon there is no air. Describe how a hammer and a feather dropped together would fall.

Answers and look-fors

• Part A: about 1 N for 100 g and 9.8 N for 1 kg; each kilogram weighs about 9.8 N. Weights: earth 588 N, the moon 96 N, mars 222 N, jupiter 1488 N.
• Part B: 1. weight only (air resistance tiny): speeds up. 2. weight larger than air resistance: still speeds up, but less. 3. weight and air resistance equal: steady speed. 4. air resistance much larger than weight: slows down until the two balance again, at a lower steady speed.
• Part C: 1. Its mass is the same everywhere; its weight depends on the gravitational field strength. 2. As it speeds up, air resistance grows until it equals the weight; the net force is then zero, so the speed stops changing. 3. The open parachute has a much bigger area, so air resistance is far greater at the same speed, and balance comes at a much lower speed.
• Exit ticket: 1. 588 N. 2. Kilograms; newtons. 3. The weight and the air resistance are balanced.
• Bigger: with no air resistance, both fall with the same acceleration and land together, as an astronaut showed on the Moon in 1971.

Weight and falling

A. Weigh it

W = m g. Work out the weight of a 60 kg student on each world.

B. The skydiver

For each stage, draw the skydiver as a dot with an arrow for the weight and an arrow for the air resistance, to scale. Then say what happens to the speed.

C. Questions

Exit tickets

Designing for safety

In a crash, a passenger must lose all their speed. The acceleration is the change in speed divided by the time it takes, so the longer the stop takes, the smaller the acceleration, and by F = m a the smaller the force on the body. Crumple zones, seatbelts that stretch a little, and airbags all make the stop last longer. A 70 kg passenger stopping from 15 m/s (54 km/h) in a hundredth of a second feels a force of about 105 000 N; spread over 0.15 s it is about 7 000 N. Students work out the forces, then design packaging that stops an egg as gently as possible.

We are learning to

• use a = change in speed ÷ time and F = m a to work out the force in a collision,
• explain how car safety features reduce the force on passengers,
• design, test and improve a solution to a problem.

Success criteria

• I can work out the force on a passenger for different stopping times.
• I can explain how my egg packaging made the stop last longer.

You need

• for each group: a raw egg sealed in a zip-lock bag, packing materials (paper, straws, cotton wool, tape), a metre ruler; a sheet of plastic on the floor; students with an egg allergy take another role, and everyone washes their hands afterwards,
• the worksheet (next sheet), one per student, and the class results sheet (third sheet), on the board or a bench.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the catch, the board and Part A in Session A, and the egg challenge and Part C in Session B.

Watch for these ideas

• “A stronger, stiffer car is safer.” A car that crumples makes the stop last longer, so the force on the people inside is smaller.
• “Airbags stop you hitting things.” They slow you more gradually and spread the force over a larger area.
• “The force depends only on the speed.” It also depends on how quickly the speed is lost.

Make it easier, make it bigger

• Easier: work out the acceleration for the first stop together, then students use F = m a for all three.
• Bigger: why do helmets, gym mats and the sand in a long jump pit all protect the body? Use the same idea.

Answers and look-fors

• Part A: hitting a hard dashboard: a = 15 ÷ 0.01 = 1 500 m/s², F = 105 000 N; held by a seatbelt: a = 15 ÷ 0.08 = 187.5 m/s², F = 13 125 N; seatbelt, airbag and crumple zone: a = 15 ÷ 0.15 = 100 m/s², F = 7 000 N. The longer stop gives about 15 times less force than the hard dashboard.
• Part B: results vary; the best designs crumple or cushion, so the egg stops over a longer distance and time.
• Part C: 1. The same speed is lost over a longer time, so the acceleration and the force are smaller. 2. The passenger keeps moving forwards (first law) until the belt stops them; the belt stretches a little, making the stop longer. 3. It folds, so the car takes longer to stop; the cabin stays strong so it does not crush the people inside.
• Bigger: each makes the stop take longer, and spreads the force, so the force on the body is smaller.

Designing for safety

A. Three stops

A 70 kg passenger stops from 15 m/s (54 km/h). Acceleration = change in speed ÷ time. Force = mass × acceleration.

B. Protect the egg

The egg stays sealed in its bag. Design packaging in 10 minutes, then drop it from each height. Stop when the egg cracks.

C. Questions

Class results: the egg challenge

Each group adds its design in a few words and the highest drop its egg survived. Which features do the best designs share?

Link each good feature to the physics: a longer stopping time means a smaller force.

Show what we know

The term comes together. In the task, a 50 kg student stands on scales that read in newtons, in a lift. The scales read the force they push up with. When the lift is still or moving steadily, that force balances the weight; when the lift speeds up going up, the scales must push harder, to give a net force upwards; when it slows near the top, they push less. Students predict and explain the four readings with all three laws. Then they sit the eight-question final check, and the class plays the unit quiz as a game on the board.

We are learning to

• apply all three laws to one situation,
• calculate a force from the mass and the acceleration,
• explain readings with net force and force pairs.

Success criteria

• I can predict and explain each scale reading in the lift.
• I can answer the final check on my own.

You need

• the task (next sheet) and the final check (third sheet), one each per student; calculators,
• the interactive unit open on the board for the quiz; mini whiteboards if you have them.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the laws and the task in Session A, and the final check and the quiz in Session B.

Watch for these ideas

• Students who think the reading rises while the lift moves up steadily: steady motion needs no net force.
• Students who say the weight changes in the lift: the weight is the same; the push of the scales changes.
• Students who call the weight and the push of the scales a third law pair: they act on the same student.

Make it easier, make it bigger

• Easier: give the net force for each part, so students add it to the weight.
• Bigger: a lift going down starts off. What does the scale read, and why?

Answers and look-fors

• Task table: standing still at the ground floor: net force 0 N, reading 490 N; starting to go up: net force 60 N, reading 550 N; moving up at a steady speed: net force 0 N, reading 490 N; slowing down near the top: net force -60 N, reading 430 N.
• Task questions: 2. The lift and student speed up upwards, so there must be a net force upwards: the scales push up 50 × 1.2 = 60 N more than the weight. 3. Moving steadily, the forces balance (first law), so the reading equals the weight. 4. The student pushes down on the scales with exactly the force the scales push up on the student (third law). 5. Zero: both would fall together, so the scales would not push at all.
• Final check: 1. it keeps the same speed and direction. 2. 25 N to the right. 3. 5 m/s². 4. 4 m/s². 5. 15 kg. 6. the water. 7. 490 N. 8. It makes the driver stop over a longer time, so the acceleration, and the force (F = m a), are smaller; it also spreads the force over a larger area.
• Bigger: a lift starting downwards speeds up down, so the net force is down: the scales read less than the weight.
• Mark the task against the rubric in the assessment kit; the check covers net force and all three laws.

Scales in a lift

A 50 kg student stands on bathroom scales that read in newtons, in a lift. The scales show how hard they push up on the student. A phone app measured the lift’s acceleration in each part of the ride (up is positive). These are example values. Take g as 9.8 N/kg.

Net force = mass × acceleration. Scale reading = weight + net force (weight = m g).

Show what we know