Newton's Laws and Transportation Safety
Start Here
This is a paper investigation. You will read a short passage, study a force diagram and a data table, and answer questions using a pencil. You do not need a computer, a lab, or any materials besides this packet and a pencil. There are no hazards — nobody moves or builds anything. Work by yourself and do your best thinking. Write in complete sentences where you are asked to explain. If a question is hard, skip it, keep going, and come back. Reading the passage quietly aloud to yourself is allowed and encouraged.
Start Notice & Wonder 5 min
Think about what your body feels when a moving vehicle suddenly slows or stops.
1A school bus is rolling forward at a steady speed when the driver hits the brakes hard. Riders feel themselves lurch forward in their seats even though nothing pushed them from behind. Write one thing you notice and one thing you wonder about this.
2Name two safety features in a car or bus that are meant to protect people during a sudden stop or a crash. For each one, say in a few words what you think it does.
Build Read the Science 5–10 min
Newton's three laws of motion
A force is a push or a pull. When several forces act on an object, they add up to a single net force — the overall push or pull once you combine them. If the forces balance (net force is zero), the object's motion does not change. Sir Isaac Newton described how forces and motion are connected in three laws:
- First Law (inertia) — an object keeps doing what it is doing (staying still, or moving at a steady speed in a straight line) unless a net force acts on it. Inertia is this tendency to resist a change in motion. Inertia is not a force; it is a property that every object with mass has. More mass means more inertia.
- Second Law (F = ma) — the net force on an object equals its mass times its acceleration (how quickly its speed or direction changes): F = m × a. For the same mass, a bigger force causes a bigger acceleration. For the same force, more mass means less acceleration.
- Third Law (action–reaction) — for every force, there is an equal and opposite force. If object A pushes on object B, then B pushes back on A with the same size force in the opposite direction. These two forces act on different objects, so they do not cancel each other out.
Key idea for safety: in a sudden stop, the vehicle is pushed to a stop by braking friction, but a rider's body tends to keep moving forward because of inertia. Safety features work by applying forces that slow the rider more gently or spread the force out.
Word Bank
- force
- a push or a pull on an object, measured in newtons (N).
- net force
- the single overall force left after all forces are combined.
- inertia
- an object's resistance to a change in its motion (not a force).
- acceleration
- how quickly speed or direction changes, in m/s².
- action–reaction
- paired forces, equal in size and opposite in direction, on two different objects.
3In Figure 1, the passenger's body tends to keep moving forward during the stop. Which of Newton's three laws explains this, and what is the name of the property shown by the dashed arrow?
Apply Use the Data 20–25 min
A safety team recorded data from repeated braking tests using crash-test dummies. Study Table 1, then answer. (These are original numbers for this packet.)
| Starting speed (m/s) | Stopping distance (m) | Peak force on dummy — WITH seatbelt (N) | Peak force on dummy — NO seatbelt (N) |
|---|---|---|---|
| 10 | 8 | 1,600 | 4,200 |
| 15 | 18 | 2,700 | 7,000 |
| 20 | 32 | 4,000 | 10,500 |
4Observation vs. inference. Read each statement. Write O if it is an observation (something directly measured or read from the table) or I if it is an inference (a conclusion you reason out).
____ a) At 20 m/s, the stopping distance was 32 m.
____ b) The seatbelt lowers the peak force because it spreads the stop over more time and area.
____ c) With a seatbelt at 15 m/s, the peak force was 2,700 N.
____ d) A rider with no seatbelt would be hurt worse because the force on their body is much larger.
5Which law explains each observation? For each, write First (inertia), Second (F = ma), or Third (action–reaction), and one short reason.
5a. When the brakes lock, the car slows but an unbelted rider keeps sliding forward until something stops them.
5b. At a higher starting speed, the same braking force produces a much longer stopping distance.
5c. As the seatbelt pushes back on the rider, the rider pushes forward on the seatbelt with an equal force.
6Compute with F = ma. During one stop, the 50 kg dummy decelerates (slows) at 8 m/s². Use F = m × a to find the net force needed to stop it. Show your work.
6b. A larger 80 kg dummy is stopped at the same 8 m/s². Compute the net force for it. Which dummy needs a larger force, and why?
7Which safety feature and why. Pick ONE of these features — seatbelt, crumple zone, airbag, or headrest — and explain in 2–3 sentences how it reduces the force felt by a rider. In your answer, use the idea that spreading a stop over more time or more area lowers the peak force, and connect it to Newton's laws.
Explain Claim–Evidence–Reasoning 5–10 min
Question 8. A city is choosing one design change to make its school buses safer in sudden stops. As a young engineer, recommend one change (for example: require lap-and-shoulder seatbelts, add padded high seatbacks/headrests, or build in crumple zones). Write a claim, support it with two pieces of evidence from Table 1 or Figure 1, then explain your reasoning using Newton's laws.
Sentence stems you may use: "The city should… because…" · "One piece of evidence is… (from Table 1 / Figure 1)." · "A second piece of evidence is…" · "This reduces the force on riders because Newton's ___ Law says…"
Close ACE Wrap-Up 5 min
Explain one of Newton's laws (first, second, or third) in your own words, as if teaching a friend.
Point to one row of Table 1 or one arrow in Figure 1 that shows that law in action. Name it.
Give a new example of that law from somewhere outside of a car or bus.
Continue Early Finisher optional · ~15 min
Predict a change. On the back of this page, use F = ma and Table 1 to reason about ONE change: What would happen to the peak force on the dummy if the starting speed doubled from 10 m/s to 20 m/s? Would the force roughly double, more than double, or stay the same? Use the numbers in Table 1 to support your prediction, then explain why using inertia and F = ma. Then predict how a heavier rider (say 80 kg instead of 50 kg) at the same speed would change the force, and why.