Question 1

What is impulse?

Accepted Answer

Force multiplied by the time it acts, measured in newton seconds. Impulse equals the change in momentum an object experiences, which is why the two share units. A small force over a long time can produce exactly the same momentum change as a large force applied briefly — and that equivalence is the basis of most impact protection.

Question 2

How does impulse explain airbags and crumple zones?

Accepted Answer

In a crash the momentum change is fixed: the occupant must go from travelling to stationary. Impulse says force times time equals that fixed change, so extending the time reduces the peak force. An airbag lengthens the stop from milliseconds to tens of milliseconds, cutting the force by roughly the same factor. Crumple zones do the same by deforming progressively rather than stopping rigidly.

Question 3

Why do you bend your knees when landing?

Accepted Answer

To extend the stopping time. Landing stiff-legged brings you to rest in perhaps 50 milliseconds; bending the knees stretches it to 300 or more, cutting the peak force by a factor of six. The same principle governs catching a cricket ball with hands moving backwards, gymnasts rolling on landing, and the padding under playground equipment.

Question 4

What is the relationship between impulse and momentum?

Accepted Answer

They are the same quantity viewed differently: impulse is what you apply, momentum change is what results. The impulse-momentum theorem states FΔt = mΔv. Rearranged for force, it shows why the duration of an interaction matters as much as its magnitude — a point that force alone never reveals.

Question 5

How is impulse calculated when force is not constant?

Accepted Answer

It is the area under the force-time graph. Real impacts have a force that rises and falls rather than staying constant, so the average force times the duration gives the impulse. Instrumented crash tests measure exactly this curve, and safety design is largely about flattening its peak while keeping the same total area, since the area is fixed by the momentum change.

Question 6

Does impulse apply to propulsion as well as impacts?

Accepted Answer

Yes. Rocket engines are rated by specific impulse — impulse per unit of propellant — because what matters is total momentum imparted, not instantaneous thrust. A low-thrust ion engine firing for months can deliver more total impulse than a chemical rocket burning for minutes, which is why deep-space missions use them despite their feeble push.

Impulse Calculator

Everyday Uses

Impact forces

Safety design

Linking force, time and momentum

Propulsion

Rolling with a punch

The egg drop challenge

Frequently Asked Questions

What is impulse?

How does impulse explain airbags and crumple zones?

Why do you bend your knees when landing?

What is the relationship between impulse and momentum?

How is impulse calculated when force is not constant?

Does impulse apply to propulsion as well as impacts?

Related Calculators

Everyday Uses

Impact forces

Safety design

Linking force, time and momentum

Propulsion

Rolling with a punch

The egg drop challenge

Frequently Asked Questions

What is impulse?

How does impulse explain airbags and crumple zones?

Why do you bend your knees when landing?

What is the relationship between impulse and momentum?

How is impulse calculated when force is not constant?

Does impulse apply to propulsion as well as impacts?