14. Force, Momentum and Impulse

Question 1

How can Newton’s second law be written in terms of momentum?

Answer 1

F = (mv - mu) / Δt

“Force is rate of change in momentum”

F = resultant force (N)
m = mass (kg)
u = initial velocity (m/s)
v = final velocity (m/s)

Question 2

What is impulse?

Answer 2

The product of force and time

Question 3

What is the equation for calculating impulse?

Answer 3

F Δt = Δ (mv)

F Δt = impulse (Ns)
Δ (mv) = change in momentum (kg m/s)

Question 4

What does the area underneath a force-time graph represent?

Answer 4

Impulse

Question 5

How can the force of an impact be reduced?

Answer 5

Increasing the time of the impact

Question 6

Name 3 examples of when impact force is reduced

Answer 6

1. The less time your foot is in contact with a football when kicking it, the more force you kick it with (assuming change in momentum is the same)
2. Packaging for fragile objects is designed to reduce magnitude of any impact forces during transport or storage. Packaging takes longer to deform on impact, so absorbs shock and protects packaged object

Question 7

Name 3 examples of vehicle safety design

Answer 7

1. Seat belts stretch slightly increasing time for wearer to stop and reduces forces acting on chest
2. Air bags slow down passengers more gradually and prevent them hitting hard surfaces in car
3. A car’s crumple zones that extend time of collision