# Bow & Arrow: Potential to Kinetic Energy

By Ham Sandwich

Topic: Physics & Chemistry

[Open the interactive Jig](https://ask.jig.com/j/yRKrTohjkU59)

## Guide

### 1. An energy machine from the Middle Ages

On a summer meadow, an English longbow waits on its stand beside the practice butt\. A bow is a simple machine for moving energy: your arm puts it in slowly, and the bow hands it to an arrow in an instant\.

Drag anywhere on the meadow to look around\. The string is yours to pull in every step\.

### 2. Potential energy: stored by bending

As the string comes back, the limbs bend\. The side facing the target stretches and the side facing the archer squeezes, like a spring\. That stored energy of shape is potential energy, glowing amber in the limbs and climbing on the board\.

The string itself stores very little\. The wooden limbs do the storing\.

### 3. Let go: potential becomes kinetic

Release, and the limbs spring forward, pushing the string and arrow\. In about a hundredth of a second, stored potential energy becomes kinetic energy, the energy of motion\. Watch the amber bar fall as the blue bar rises\.

Kinetic energy is one half of the mass times the speed squared\. The flight here is slowed down\.

### 4. Pull back and feel the difference

Drag the string back yourself, or set the draw with the slider, then let go\. On the board, the energy stored is the shaded area under the force curve\. Twice the draw stores about four times the energy, so the arrow strikes harder and sinks deeper\.

### 5. Three bows of history

The English longbow of the Hundred Years War was a tall stave of yew\. Greek and Roman archers used short composite bows of wood, horn and sinew\. Mongol bows had stiff, upright ears that work as levers\. Pick one and shoot to compare\.

Composite bows pull hard early in the draw, so their force curve is fuller and stores more energy per pound of peak weight\. Values are illustrative\.

### 6. What the bowstring adds

Medieval strings were linen or hemp; silk and sinew were used on composite bows\. A string barely stores energy, but a stretchy, heavy string soaks some up and moves slowly, so less reaches the arrow\. Compare the blue bar after each shot\.

The limbs always do the storing\. A stiff, light string delivers the largest share to the arrow\.

### 7. Where the energy goes

Your arm did work to bend the bow\. The limbs stored it as potential energy, the arrow carried it as kinetic energy, and the target took it as work, crushing straw as the arrow stopped\. Some was lost on the way as vibration, sound and heat\.

Energy is never used up, only moved from one form to another\.