Torque and the Moment Arm
Explained Simply for Elementary PE
Hello, this is Young-in teacher! :)
Throwing a ball, swinging a bat, throwing a disc…
Behind many movements in PE class lies an important principle of force called torque.
“Why is the door handle placed at the very edge?”
“Why is it easier to hit a single when you choke up on the bat, but harder to hit a home run?”
Today, we’ll uncover the secrets of torque and the moment arm in a way that makes sense for elementary students!
1️⃣ What is torque?
Torque is the turning effect of a force — the tendency of a force to make an object rotate.
In physics, we write it as:
Torque = Force × Moment Arm
But for children, you can explain it like this:
“Even if you push with the same strength,
if you push farther away from the center of rotation,
it will turn much more easily!”
That’s why we push on the door handle, which is far away from the hinges (the axis of rotation), when we open a door. We can create large torque with relatively little force.
2️⃣ The meaning of the moment arm: “The magic of distance”
The moment arm is the distance from the axis of rotation to the point where the force is applied.
If you push close to the axis:
→ The moment arm is short → It doesn’t rotate well (you need a lot of force)
If you push far from the axis:
→ The moment arm is long → It turns more easily (large torque is produced)
You can apply this directly in tee-ball or baseball lessons in elementary PE:
Holding the bat near the end:
→ The moment arm is long → You can generate greater torque (more power, long hits).
Choking up and holding the middle of the bat:
→ The moment arm is shorter → Torque is smaller, but control is easier (better contact, easier to aim).
You can tell students:
“If you hold the bat longer (near the end), you can amplify your strength and send the ball farther!”
Their eyes will light up. ✨
3️⃣ Our body is also “a lever + axis of rotation”
The joints in our body act like axes of rotation.
Bending your elbow to lift a dumbbell
Rotating your shoulder to throw a ball
Extending your knees to jump
All of these are actually rotational movements.
In these cases, the muscles pull on the bones to create torque:
Muscle force × Distance to the point of force application
= Torque, which makes the arms and legs swing and rotate.
4️⃣ Explanations you can use directly in class (Throwing & Swinging)
Once you know this concept, your movement instruction becomes much more scientific.
Throwing a ball
“Stretch your arm out and make a big swing!
When your arm gets longer (moment arm increases), the same force creates more torque to send the ball farther.”
Throwing a flying disc
“Don’t just flick your arm. Rotate your whole body as you throw!
You need to create big torque starting from your body’s center for the disc to fly ‘whoooosh~’ through the air.”
� Classroom Application – Young-in Teacher’s TIP! (Use it right away)
✅ Tip ① Introduce the concept with a “door handle experiment”
Use the classroom door. Have a student try pushing the door with one finger at:
Right next to the hinges
The middle of the door
The door handle
Then ask:
“Where did it turn the easiest?”
Connect the difference in distance to the idea of the moment arm.
Kids can understand the principle in just one minute.
✅ Tip ② Bat/racket grip experiment
Have students compare:
(A) Swinging with a very short grip
(B) Swinging with a very long grip
Let them feel:
“Which one feels heavier and more powerful when it turns?”
“Which one feels lighter and easier to control?”
They will experience the balance between torque (power) and control with their own bodies — a perfect applied biomechanics lesson.
� In Closing
“When you know the science, PE becomes easier!”
Torque and the moment arm are keys that help children learn how to use their strength more efficiently. In today’s PE class, instead of just shouting “Harder!”, try giving a scientific tip like:
“How about holding it longer and making a bigger swing?”
It’s a small change in words, but a big step toward science-based PE.
