Week 14 · Axis 2, Unit 2 Motion, Concept 2.3 Energy and Collisions (B) and Unit Project “Vehicle Safety” · 3 lessons
3
Keeping passengers safe
Discovery Education Science P4: Term 1, Unit 2, pp. 172–188
GoalExplain how seat belts, airbags and head restraints protect passengers, and test a crash-protection idea safely.
New words
seat belt · a strap that holds a passenger in the seatairbag · a bag that fills with air in a crash and cushions the passengerhead restraint · the pad behind the head that stops it snapping back
Explanation
A moving object keeps moving until something stops it. When a car stops suddenly, the passengers’ bodies keep moving forward at the car’s old speed. A seat belt holds the passenger back in the seat, so the body slows down with the car. An airbag fills with air in a crash and gives a soft cushion that stops the body more slowly, which spreads the push over a longer time. A head restraint stops the head from snapping backward. Children sit in child seats in the back. Cyclists and motorbike riders wear helmets. Engineers test safety ideas with models. In a test, we change one thing, such as a seat belt, and keep the same truck, ramp and starting place. Then we write a claim, evidence and reasoning.
Safety part
What it does
seat belt
holds the body in the seat
airbag
cushions the body in a crash
head restraint
stops the head snapping back
helmet
protects the head of a cyclist
Worked examples
A bus brakes suddenly. Standing passengers lurch forward because their bodies keep moving. Passengers in seats with belts stay in their seats and slow down with the bus.
Salma tests a model. A toy truck with a clay person rolls down a ramp into a book. With no belt the clay person flies forward 30 cm. With a paper-strip belt it moves only 5 cm. The belt made 30 − 5 = 25 cm less movement.
Claim
Evidence
Reasoning
a belt protects
5 cm and 30 cm
body keeps moving; belt holds it
Claim: a seat belt protects a passenger. Evidence: in the test the figure with a belt moved 5 cm and the figure without a belt moved 30 cm. Reasoning: a moving body keeps moving when the car stops; the belt holds it back and slows it with the car.
Class activity
Seat-belt model. A grown-up helps. Make a small clay person and sit it in a toy truck or a box on wheels. Roll the truck down a low ramp into a book, with no belt, and measure how far the clay person moves forward. Then add a strip of paper as a belt and repeat from the same place. Record both. Never test with a real person or pet, and keep faces away.
Practice
1
A car stops suddenly. Why do the passengers lurch forward?
Their bodies keep moving at the old speed until something stops them.
2
Which two parts protect a passenger in a crash? Say the letters.
Letter
Part
A
seat belt
B
radio
C
airbag
A and C: the seat belt and the airbag.
3
In the model test, which thing do you change? Which things stay the same?
Change only the belt. Keep the truck, the ramp and the starting place the same.
4
Name two ways to stay safe in a car or on a bicycle.
Wear a seat belt, sit in a child seat in the back, wear a helmet on a bicycle.
