Newton's laws explain why safety features and techniques work. Seat belts and head restraints deal with inertia (first law); airbags and crumple zones lengthen the stopping time to cut the force (F = ma); rockets push gases back and are pushed forward (third law); and a spearthrower (woomera) extends the thrower's arm so the force acts for longer and over a greater distance, so the spear leaves faster.
A crash test dummy hits an airbag and the force on it is far smaller than hitting the dashboard. Same crash, same dummy. What does a bag of air change?
A short lesson with no simulation. You have all three laws. Here you use them to explain things people have designed.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: the airbag
ExplainUse the particle model to explain what you saw.
Explain: design with the laws
In your book: choose a real design (helmet, seat belt, rocket, kicking technique or a woomera). Say which of Newton's laws it uses and explain in two sentences how.
Match each feature to the law that explains it.
Seat belt keeps you in your seat when the car stops
Airbag spreads the stop over more time
Rocket gases go down, rocket goes up
A heavier ball is harder to accelerate
A 1000 kg car going 20 m/s is stopped by crumple zones in 0.5 s. What is its acceleration (m/s², size only)?
What average force is needed to stop it (N, size only)?
Elaborate TypicalUse the same idea in a new context.
Elaborate: sport
Elaborate WiderUse the same idea in a new context.
Elaborate: braking by itself
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
First law (inertia): seat belts and head restraints stop passengers carrying on moving when the car stops.
Second law: airbags and crumple zones lengthen the stopping time, so the acceleration and the force are smaller. A spearthrower extends the push, so the spear gets a higher launch speed.
Third law: a rocket pushes gas back and the gas pushes the rocket forward.
Numbers show how much a design helps: twice the stopping time halves the force.
For teachers
Students apply Newton's laws to design features and techniques, explain how a First Nations spearthrower extends the force on a spear, and evaluate a vehicle safety feature using F = ma (AC9S10U05, node 8, an integration node). About 20 minutes.
I can use two of Newton's laws to explain a real design or technique.
I can explain how a spearthrower works in terms of force, time and acceleration.
I can compare two safety designs with F = ma.
Before class
An integration tutorial with no simulation that closes the unit on Newton's laws. Set the width with ?width=minimum, typical (default) or wider. Its main output is the in-your-book task, and it works best with a class discussion of a real object.
The woomera (spearthrower) is used by many First Nations peoples across Australia. Give it the respect due to a technology that is still used and still made: invite a speaker, or use resources produced with First Nations communities, and let students explain the physics without claiming to explain the culture. The lesson uses it as a lever that lengthens the push on the spear. Other design details, including how it is made, are matters for the people who hold that knowledge.
Numbers are chosen to be clean. Real crashes involve complicated forces; the lesson uses average forces.
Running the lesson
Engage: tally the predictions. Ask the 'absorbs it all' group where the energy goes.
Explain: the match and the crumple-zone calculation are the success criteria.
In your own words: a design, the law it uses and two sentences.
The hard part (on purpose)
Choosing the right law for the situation. When a student says 'Newton's laws' in general, ask which law matters for this feature and what quantity changes.
When students get stuck
A student says the airbag makes the force disappear. Ask: What is the change in speed, and how long does it take with and without the bag? Fix: The speed change is the same. A longer time means a smaller acceleration and a smaller force.
A student says a woomera makes the spear lighter. Ask: Does the spear's mass change? Fix: No. The thrower's push acts over a longer distance and time, so the speed at release is higher.
Stretch and support
Stretch: A 0.8 kg spear is accelerated by an average net force of 40 N for 0.6 s (by hand) or 0.9 s (with a woomera). Find the speed at release in each case. (30 m/s and 45 m/s: a = F ÷ m = 50 m/s², v = at.)
Support: Give each feature on a card and the three laws on three more, with a sentence frame: 'It uses the ___ law because ___ changes.'
Where it leads
Next: the Year 10 energy and climate lessons.
In class: crack an egg-drop challenge with different crumple designs; collect measurements of a ball's launch with and without a follow-through; look at a tennis racquet or cricket bat.
What each step is for
Engage: the airbag: Students say an airbag 'cushions' the blow. The law-based explanation is that it spreads the stopping over a longer time, which cuts the acceleration and so the force.
Explain: design with the laws: Applying more than one law to a design feature, explaining a First Nations technology and evaluating a safety feature with numbers are the node's three success criteria.
Elaborate: sport: Sport techniques apply the laws to the human body and show how the follow-through lengthens the time of the force.
Elaborate: braking by itself: A driverless braking system needs the laws and numbers, not just sensors.
Now you can
Use two of Newton's laws to explain a real design or technique.
Explain how a spearthrower works in terms of force, time and acceleration.