C. Matter and Energy · Forces Causing Movement

Staying Safe from Forces: Design a Safety Device

C1.2 A1.3 A1.4About 45 minutes

Learning goals

I can describe how forces from human activities (like riding in a car, biking or playing sports) can hurt people.
I can explain how safety devices like seatbelts, helmets and pads reduce harmful forces.
I can use the engineering design process to design, build, test and improve a safety device.
I can follow safety rules during an investigation.

Words to know

safety device
Something designed to protect people from getting hurt, like a seatbelt or a helmet.

impact
When one thing hits another thing with force.

cushion
Something soft that squishes to slow down a hit, so the force is gentler.

concussion
An injury to the brain caused by a hard bump, hit or shake to the head or body.

engineering design process
Steps engineers use to solve a problem: ask, imagine, plan, build, test, improve and share.

prototype
A first model of a design, built to test it.

Click!

Every time you get into a car, you hear it: click! You buckle your seatbelt. Why does it matter so much?

If a car stops very suddenly, your body keeps moving forward. The seatbelt exerts a force that holds you back in your seat so you don't hit the seat in front of you, or worse. Today you will learn how forces from things people do can hurt us, and how clever designs keep us safe.

The car stops at the wall. With no belt, the rider keeps moving forward. A seatbelt holds the rider back in the seat.

When forces can hurt

Many things people do involve big forces. Most of the time they are fun or useful, but they can cause injuries if something goes wrong:

Riding in a car or bus: in a sudden stop or crash, passengers are thrown forward.
Biking, scootering, skating and skiing: in a fall, gravity pulls you down hard onto the ground or ice.
Sports: players can bump into each other, the boards or the ice, and a puck or ball can hit hard.
Playgrounds: a fall from the climber can hurt.
Lifting heavy things the wrong way can hurt your back.
Work sites: tools or materials can fall from above.

These hard impacts can cause bruises, broken bones and concussions (brain injuries from a hard bump to the head).

How safety devices help

Safety devices work in a few smart ways:

Hold you in place: a seatbelt, car seat or booster seat holds your body so it doesn't fly forward.
Cushion the hit: a helmet has soft foam that squishes and slows down the bump, so less force reaches your head. Airbags and pads do this too.
Spread out the force: a hard shell (helmet, shin pads, hockey shoulder pads) spreads the hit over a bigger area, so no single spot gets all of it.
Shield you: a face mask, visor or mouthguard stops a puck or ball from hitting your face or teeth.
Stop slipping: ice cleats on boots and railings on stairs use friction and grip to prevent falls.

Soft ground under playground equipment (wood chips, sand or rubber) also cushions falls.

Inside a helmet. The hard shell spreads out a bump, and the foam squishes to cushion it, so less force reaches the head.

Activity	Harmful force	Safety device
riding in a car	body thrown forward in a sudden stop	seatbelt, car seat or booster seat, airbags
biking or scootering	falling onto the road	bike helmet, wrist guards, knee pads
hockey	pucks, sticks, hitting the boards or ice	hockey helmet with face mask, mouthguard, pads
playground	falling from equipment	soft ground (wood chips, sand, rubber)
building a house	tools falling from above	hard hat, steel-toe boots, gloves
walking on ice	slipping and falling	ice cleats, boots with good treads, sand on paths

Forces from human activities and the devices that protect us

Helmet facts

In Ontario, the law says bike riders under 18 must wear a bike helmet.
Use the right helmet for the activity: bike, hockey, ski and snowboard helmets are made for different kinds of hits.
A helmet must fit snugly and be buckled.
After a big crash, a bike helmet should be replaced, because its foam has been crushed.
If you hit your head, tell an adult right away, even if you feel okay.

Worked example

Let's follow the design process

Problem: A toy rider sits on a toy car. When the car rolls down a ramp and hits a wall of books, the rider flies off. Design a seatbelt to keep the rider safe.

Ask: What is the problem? The car stops suddenly, but the rider keeps moving forward. Success means the rider stays on the car, and the belt is easy to put on and take off.
Imagine and plan: ideas: a tape belt, a ribbon belt, an elastic band belt, a cotton ball cushion in front of the rider. Draw the plan and list materials.
Build the first model (a prototype): a strip of tape across the rider's lap.
Test: Trial 1, no belt: the rider flew 30 cm. Trial 2, tape belt: the rider stayed on, but the tape was hard to take off and ripped.
Improve: use an elastic band that loops over the rider and hooks on, plus a cotton ball cushion in front. Trial 3: the rider stayed on, and the belt was easy to take on and off.
Share: explain the design and the results, using words like force, impact and cushion.

The elastic band seatbelt with a cotton ball cushion worked best. It held the rider in place and cushioned the stop. Engineers test and improve until their design works.

Just for fun

Why does the seatbelt get invited on every road trip?

Because it is so good at holding on to its friends!

Hands-on activity

Design challenge: Crash-test seatbelt

You need: a toy car or truck (or a small box with a toy car under it), a small toy figure or an eraser as the rider, a ramp (a long book or board on a stack of books), a wall of books at the bottom, and building materials: tape, string, ribbon, elastic bands, pipe cleaners, cotton balls, tissue, scraps of cloth.

Ask: test with no belt first. Roll the car down the ramp into the wall. Measure how far the rider flies.
Imagine and plan: draw two ideas for a seatbelt. Pick one.
Build your prototype.
Test it 3 times from the same ramp height. Does the rider stay on? Is it easy to buckle and unbuckle?
Improve your design and test again.
Share: show a grown-up your design and explain how it protects the rider from the force of the crash.

What to look for: without a belt the rider is thrown forward; a good belt holds the rider in place, and a soft cushion helps too. Your child should change their design after testing.

Safety: use only materials a grown-up has given you; a grown-up handles any scissors. Keep the ramp low and the floor clear, and roll the car away from people and pets.

Your turn

What happens to a passenger's body when a car stops suddenly?

How does a seatbelt help?

How does the foam in a helmet help?

Name a safety device for hockey.

Why do playgrounds have wood chips, sand or rubber under the equipment?

What should you do if you hit your head hard?

What are the steps of the engineering design process?

More practice: warm-up

What do you wear on your head when you ride a bike?

What do construction workers wear to protect their heads?

What safety device do you click every time you ride in a car?

What do we call a first model of a design?

What can you put on boots to stop slipping on ice?

More practice: on your own

Explain how a mouthguard protects a hockey player.

Why should you replace a bike helmet after a big crash?

Which force pulls a skateboarder down to the ground in a fall? Which safety devices would help?

In the design example, why did the designer test with no belt first?

Describe one human activity that can cause a harmful force and one device that reduces it.

Challenge

Why does a helmet need both a hard outer shell and soft foam inside? What does each part do?

Your seatbelt design held the rider on, but it took a long time to buckle. What would you do next, and why?

Design a safety device for a new activity: sledding down a snowy hill. Describe it and explain how it reduces harmful forces.

Check your understanding

Quiz

A car stops suddenly. Without a seatbelt, a passenger would...

How does the foam in a helmet protect your head?

Which device protects a hockey player's teeth?

Why are there wood chips or sand under a playground climber?

What should you do if you hit your head hard while playing?

In the engineering design process, what do you do after you test?

For parents and teachers

Big idea: Ontario Grade 3 expectation C1.2 asks children to assess harmful effects of forces that may result from human activities, and to describe how health and safety devices minimize them. Safety devices hold us in place (seatbelts, car and booster seats), cushion and spread impacts (helmets, pads, airbags, soft playground surfaces), shield us (face masks, mouthguards) or prevent slips (cleats, railings). The seatbelt challenge uses the engineering design process (A1.3) and safe procedures (A1.4).

How to help: Check your child's helmet together: it should sit level on the forehead, be snug, and be buckled with the straps forming a "V" under each ear. Talk about why each family member buckles up. In Ontario, cyclists under 18 are required by law to wear a bicycle helmet; ask your child's school or check Ontario's Ministry of Transportation for car seat and booster seat rules.

Concussion awareness: Grade 3 is a good age to learn that any hard hit to the head must be reported to an adult. Signs of a possible concussion include headache, dizziness, confusion, nausea and unusual tiredness; seek medical advice if you notice these.

Common difficulties:

Thinking the seatbelt "pushes" you. It pulls (holds) you back while your body tries to keep moving forward.
Stopping after the first test. Praise improvements; real engineers test many times.

Safety: supervise the crash tests, keep the ramp low, and handle scissors yourself.