01 Key Concepts
Impulse Definition
Impulse = force x time = F*t, measuring the overall effect of a force applied over a duration.
Impulse-Momentum Theorem
Impulse equals the change in momentum: F*t = (change in momentum) = m*(v_final - v_initial).
Units of Impulse
Measured in newton-seconds (N*s), which is equivalent to kg*m/s (the same units as momentum).
Extending Collision Time to Reduce Force
Since impulse (F*t) for a given momentum change is fixed, increasing the time of impact (like with an airbag) decreases the force experienced.
Impulse from a Force-Time Graph
The area under a force-time graph represents the total impulse delivered, even for forces that change over time.
02 Key Formulas
- Impulse = F*t = m*(v_final - v_initial)
03 Solved Examples
Example 1 A 10 N force acts on an object for 3 seconds. Find the impulse delivered.
- Apply Impulse = F*t = 10*3.
Answer: 30 N*s
Example 2 A 2 kg ball changes velocity from 3 m/s to 9 m/s due to a force applied for 4 seconds. Find the average force.
- Apply F*t = m*(v_final-v_initial): F*4 = 2*(9-3) = 2*6 = 12.
- F = 12/4.
Answer: 3 N
Example 3 Explain why bending your knees when landing from a jump reduces the force on your body.
- Your change in momentum (from moving to stopped) is fixed by your mass and landing speed.
- Bending your knees extends the time over which you decelerate.
- Since impulse (F*t) is fixed, a longer time means a smaller average force.
Answer: Bending your knees increases the stopping time, which reduces the average force for the same momentum change
04 Practice Questions
1A 5 N force acts for 6s. Find impulse.
30 N*s
2A 1 kg object's velocity changes from 2 to 8 m/s in 3s. Find the average force.
F*3=1*6=6, F=2N
3What theorem relates impulse to change in momentum?
The impulse-momentum theorem
4Why do airbags reduce injury in car crashes?
They extend the time of impact, reducing the average force for the same change in momentum
5What are the units of impulse?
N*s (equivalent to kg*m/s)
📄 Impulse — Downloadable Worksheet
10 questions with a full answer key. Grab the PDF to print, or try the interactive version in your browser.