Springs Store Energy

Lesson 8 of 10 · 7 min · Free, no account needed

What you will learn

Hooke's law: a spring pulls back with F = k × x. x is the stretch in metres, k the spring constant in N/m.
k is the slope of the force line: a stiffer spring has a steeper line.
A stretched spring stores elastic energy E = ½ × k × x²: twice the stretch stores 4 times the energy.

Pull a slingshot twice as far. Does the stone fly twice as far, or more?
A 10 cm pull lands at the green flag. Drag your flag to where a 20 cm pull lands.
Stretch the spring with the hook. Watch the force meter and the graph.
A soft spring and a stiff one. Stretch both.
Springs follow a simple law.
Hooke's law: F = k × x. The spring constant k, in N/m, says how stiff the spring is.
Stretching it is work against a force that grows from 0 to kx, so the work is the triangle under the line: E = ½ × k × x², the elastic energy.
Simplified model: an ideal spring. Real springs and bands stop obeying F = kx if you stretch them too far.
Knock over the can at 6.8 m. Dial the pull, then Check to fire.
Game: Pinball plunger. Stop the ball in each target zone.
Your spring from step 2, k = 200 N/m, sends the ball up the tilted table.
Math: F = kx is a line y = mx with slope k. Tap the spring with k = 200 N/m.
A spring with k = 200 N/m is stretched 0.1 m. How much energy does it store, in joules?
Replay your three jackpot shots. Press Play.

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