D. Structures and Mechanisms · Forces Acting on Structures

Protective Equipment: Helping Our Bodies Withstand Forces

D2.5 A1.2 A1.4 A3.1About 45 minutes

Learning goals

I can describe four ways protective equipment protects people from harmful forces.
I can explain how the parts of a helmet work together.
I can match protective equipment to the forces it protects against in sports, travel and work.
I can test how padding and hard shells change the force of a hit.

Words to know

protective equipment
Things people wear or use to protect their bodies from harm, like helmets, pads, mouthguards and seatbelts.

impact
A hard hit or collision between two things.

absorb
To soak up. Foam absorbs some of the energy of a hit by squishing.

spread a force
To share a push over a bigger area, so each spot gets less of it.

concussion
A brain injury caused by a hard bump, hit or jolt to the head.

certified
Tested and approved to meet a safety standard. Look for a safety label on helmets.

Your body is a structure too

Your skeleton holds you up like a frame. Your skull is a dome that protects your brain, and your ribs form a cage around your heart and lungs. But bodies can be hurt by big forces: a fall off a bike, a hit in hockey, a sudden stop in a car.

Just like engineers add features to buildings, people add protective equipment to their bodies.

Remember from Grade 3

In Grade 3 you learned that safety devices hold you in place, cushion a hit, spread out a force and shield you. In Grade 5 you will look more closely at how they change forces, and test it yourself.

A bike helmet, a hockey helmet with a cage, knee pads, elbow pads and a shin guard laid out on a wooden bench. — Each piece has a hard outer shell to spread out a force and soft padding inside to cushion a hit. AI-generated image

Four ways protective equipment works

Spread the force. A hard shell (on a helmet, shin pads, a hard hat) spreads a hit over a bigger area. The same force shared by more of your body means less force on each spot. It's like snowshoes: they spread your weight over more snow, so you don't sink.
Cushion and slow the stop. Soft foam or padding squishes during a hit. Squishing makes your body stop more slowly, over a longer distance. A slower stop means a smaller force on your body. Airbags and gym mats work this way too.
Hold the body in place. Seatbelts, booster seats and safety harnesses hold you so you don't fly forward or fall. A seatbelt spreads the force across the strongest bones of your body: your hips, chest and shoulder.
Shield from hits and crushing. Face cages, visors, mouthguards and steel-toed boots block hard objects, like a puck or something heavy dropped on a foot.

A snowshoe spreads your weight over a bigger area, so each bit of snow is pushed less. A helmet's hard shell spreads a hit the same way.

Inside a bike helmet (seen from the side, cut in half). The hard shell spreads the hit over a big area, and the foam underneath crushes to slow the head down more gently.

Helmets: two layers working together

The hard outer shell spreads the hit and lets the helmet slide on the ground instead of catching.
The foam liner crushes during a crash. This is a big reason a bike helmet should be replaced after a crash: crushed foam can't protect you again, even if the outside looks fine.
Helmets are made for different activities. A hockey helmet is built for many hits; a bike helmet is built for one big crash. Use the right one, and look for a certified safety label.
A helmet only works if it fits. Many Canadian safety groups teach the 2V1 check: about 2 fingers' width between your eyebrows and the helmet, the straps make a V under each ear, and only 1 finger fits under the buckled chin strap.

Equipment	Where it is used	How it protects
bike or ski helmet	biking, skiing, snowboarding	shell spreads the hit; foam cushions
hockey helmet with face cage	hockey	cushions hits; cage shields the face from pucks and sticks
mouthguard	hockey, basketball, many sports	cushions and spreads hits to the teeth and jaw
wrist guards and knee pads	skateboarding, in-line skating	hard pieces spread the force; padding cushions falls
seatbelt and booster seat	cars and trucks	hold the body in place; spread force across strong bones
airbag	cars and trucks	cushions and slows the body
hard hat	construction sites	shell spreads the force of falling objects
steel-toed boots	construction, factories, farms	steel cap shields toes from crushing
safety harness	work on roofs and towers	holds a worker so a fall is stopped

Protective equipment and how it works

Worked example

Let's explain a gym mat

Why does falling onto a thick gym mat hurt much less than falling onto the hard gym floor?

Both times, your body is moving and has to stop.
On the hard floor, you stop almost instantly. A very fast stop means a big force on your body.
On the mat, the foam squishes, so you stop more slowly, over a few centimetres. A slower stop means a smaller force.
The mat also touches a bigger area of your body, so the force is spread out.

The mat cushions (slows the stop, so the force is smaller) and spreads the force over more of your body.

Worked example

Let's choose equipment for a job

A roofer is replacing shingles on a two-storey house. What protective equipment should they wear, and which force does each protect against?

Falling is the biggest danger: a safety harness attached to a strong anchor holds the worker and stops a fall (gravity).
Tools or shingles could drop from above onto workers below: a hard hat spreads that force.
Heavy bundles could land on feet: steel-toed boots shield the toes from crushing.
Gloves protect hands from scrapes and cuts.

Safety harness (falls), hard hat (falling objects), steel-toed boots (crushing), gloves (scrapes and cuts).

Just for fun

Riddle: What did the helmet say to the head?

"Don't worry, I've got you covered!"

Hands-on activity

Dent test: shell versus foam

You need: play dough or modelling clay, a rolling pin or a can to flatten it, a ruler, a full, unopened small can (like a tuna can), a kitchen sponge, a square of thin cardboard (about 8 cm by 8 cm), and a tray.

Flatten the play dough into a smooth pancake about 2 cm thick on the tray. This is your "head".
No protection: hold the can 10 cm above the dough, flat side down, and let it drop straight down. Measure how deep the dent is. Smooth the dough again.
Shell only: lay the cardboard square on the dough. Drop the can from the same height. Lift the cardboard and measure the dent.
Foam only: lay the sponge on the dough. Drop the can. Measure.
Shell and foam: sponge on the dough, cardboard on top of the sponge. Drop the can. Measure.
Do each test twice and record your results in a table. Which protection made the shallowest dent? Which made the dent wider but shallower?

What to look for: with no protection the dent is deep and the shape of the can. The cardboard spreads the force, so the dent is wider and shallower. The sponge cushions, so the dent is smaller. Shell plus foam usually works best, just like a real helmet.

Safety: a grown-up should help. Drop the can only from 10 cm, keep fingers and toes out of the way, and do not open the can. Wear safety glasses if you have them, just as scientists do.

Your turn

Name the four ways protective equipment protects us.

What does the hard shell of a helmet do?

What does the foam inside a helmet do?

Why should a bike helmet be replaced after a crash?

Which protective equipment protects workers from falling objects?

What does the 2V1 helmet check mean?

More practice: warm-up

What does a seatbelt do?

Name a piece of hockey protective equipment.

What do steel-toed boots protect?

What is a concussion?

Which part of your body is a natural dome that protects your brain?

More practice: on your own

Explain why a slower stop means a smaller force on your body.

Why does a seatbelt go across your hips and shoulder, not your stomach or neck?

In the dent test, why did you drop the can from the same height every time?

A friend says, "A helmet that is too loose is fine, as long as I'm wearing one." Do you agree? Explain.

Why do hockey players wear a mouthguard?

Challenge

A car's airbag and seatbelt work together in a crash. Explain how each one changes the force on the person.

Why is a bike helmet built for one big crash, while a hockey helmet is built for many hits?

Design a piece of protective equipment for a dog that runs through bushes on hikes. Name the force it protects against and how it works.

Check your understanding

Quiz

How does the hard outer shell of a helmet protect your head?

How does the foam inside a helmet protect your head?

Why should a bike helmet be replaced after a crash?

Which equipment holds a worker so a fall is stopped?

Why does landing on a gym mat hurt less than landing on the floor?

In the 2V1 helmet check, what should make a V?

For parents and teachers

Big idea (D2.5): Protective equipment protects people from harmful forces by spreading force over a bigger area (hard shells), cushioning and slowing the stop (foam, airbags, mats), holding the body in place (seatbelts, booster seats, harnesses) and shielding (face cages, mouthguards, steel toes). Grade 3 introduced safety devices; Grade 5 explains how they change forces. The dent test is a fair test (A1.2) done safely (A1.4), and the equipment chart connects to home, sports and work (A3.1).

How to help: Check your child's helmet together with the 2V1 fit test and look for a safety certification label. Talk about why workers in the skilled trades wear hard hats, harnesses and steel-toed boots.

Common difficulties:

Saying padding "blocks" the force. The force isn't blocked; it is spread out or made smaller by slowing the stop.
Keeping a damaged helmet. Explain that crushed foam can't protect again.
Safety: supervise the dent test, drop the can from 10 cm only, and keep fingers clear. Remind your child that if they ever hit their head, they must tell an adult right away.