�Biomechanics in ElementaryPE

How Impulse Helps Students Catch Softly

Hello, this is Young-in teacher! :)

In PE class, when a fast dodgeball comes flying in, one student catches it with a loud “THUD!” and shakes their hands in pain, while another student receives the exact same ball softly and says, “It doesn’t hurt at all.”

This difference is not simply about “bravery” or having a “tough body.” It comes from a technical difference in how they spread out the impact — Impulse.

Today, let’s break down the core principle of impulse in catching and landing, in a way that’s easy for elementary students to understand!

1️⃣ What is Impulse?

In physics, impulse describes how long a force acts and how big that force is.

Impulse = Force × Time

If the object stops in a very short time (Time ↓)
→ The force (Force) becomes very large, which feels painful and increases the risk of injury.

If we spread the stopping over a longer time (Time ↑):
→ The force at any given moment becomes smaller,
→ So the same total impulse feels softer and safer.

For children, you can explain it like this:

“Imagine the ‘impact’ is 100 kg. If you try to handle all 100 kg in 1 second, it’s really hard and it hurts. But if you spread the same 100 kg over 10 seconds, it feels much easier and not so painful. Catching a ball is just like that — you spread the impact out over time.”

2️⃣ Why do we pull our arms back when catching a ball? (Increasing Time)

In dodgeball, basketball, or tee-ball, teachers often say:

“When you catch the ball, pull it in toward your chest as you receive it!”

That’s not just a nice-looking “form” — it’s physics that reduces impact.

❌ Arms locked and stiff in front: When the ball hits the hands, it stops in about 0.1 seconds. The impact is concentrated on the palms and wrists — “WHACK!” — and the ball may bounce off.

⭕ Arms moving back (cushioning): As you catch, you pull your arms back toward your body. Now the ball stops over about 0.5 seconds instead of 0.1 seconds. The same impulse is spread over a longer time, so the impact is felt as a gentle “swoosh” instead of a painful “bang.”

In other words:

Pulling the arms back while catching
= A technique for “paying off” the impact in small installments instead of all at once.

3️⃣ Impulse is just as important in landing

The same principle applies to landing from vaults, jumps, or boxes.

Stiff landing:

Landing with straight knees and a rigid body
→ The impact travels from the feet to the head almost instantly
→ The joints take a huge shock all at once.

Soft landing:

Landing with a sequence: toes → heels → bending knees → lowering hips
→ The body takes more time to come to a complete stop
→ Muscles and joints share the impact over time, making it much safer.

For students, you can say:

“Land like a cat or a spring!
Come down slowly and quietly, without making a loud sound.”

4️⃣ Easy phrases for teaching impulse in elementary PE (Magic Words)

Instead of focusing on formulas, try using simple “magic sentences” during lessons:

“If you stop suddenly, you get a big ‘BANG!’ (ouch).
If you stop slowly, it feels ‘soft and cushioned’ (safe).”

“The longer you make the ball or your body take to stop,
the less it hurts.”

“Pulling your arms back and bending your knees
is a smart way of spreading out the impact.”

Once students get this feeling in their bodies,
they’ll be able to connect it later when they learn physics in middle or high school:

“Oh! This is what we learned in PE class — Impulse!”

(Okay, maybe that’s a bit optimistic… but it really can happen! ㅋㅋ)

� Classroom Application – Young-in Teacher’s TIP! (Use it right away)

✅ Tip ① “Wall vs Blanket” Imagination & Experiment

Ask:

“If you bump into a hard wall, does it hurt?
What about bumping into a soft blanket? Why is there a difference?”

Then have students work in pairs and alternate between:

(A) Catching a ball with their arms fixed and stiff, and

(B) Catching the ball while pulling their arms back toward the body.

Ask:

“Which one felt more like a soft blanket and less painful?”

Let students discover the principle of impulse through their own experience.

✅ Tip ② “Slow-Motion Landing” Feedback

Use a low box (step box) or a small platform on the field:

Have students jump down from a safe height,

Record their landing in slow motion (tablet/phone).

Then watch together:

Look for how feet → knees → hips bend in sequence
and how long it takes for the body to come to a full stop.

Ask:

“What score would you give your landing?
What could you bend a little more to make it even softer?”

This helps students actively refine their landing technique.

� In Closing

Children who are “good at sports” often instinctively know how to cushion impact. But other children need a clear, scientific tip:

“Take more time to stop!”

In today’s PE lesson, try giving your students the gift of “soft receiving skills” — in both catching and landing. Their fear will decrease, their confidence will grow. �