Momentum & Impulse

Objectives

1. Understand the concept of momentum

2. Know how to calculate for momentum

3. Understand the concept of impulse

4. Know how to calculate for impulse

Momentum

What is momentum?

It is the quantity of motion of a moving body, measured as a product of its mass and velocity.

Think of it as inertia in motion.

Larger the mass, the harder to stop

Small mass but high velocity

Calculation of momentum

To calculate for momentum:

𝑚𝑜𝑚𝑒𝑛𝑡𝑢𝑚 = 𝑚𝑎𝑠𝑠 × 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦

𝑝 = 𝑚𝑣 Large mass and small velocity

Small mass and large velocity

P

m v

Example of momentum

A 10 kg object moving at a velocity of 3 m/s has a momentum of

p = mv

p = 10 * 3

p = 30 kg m/s = 30 Ns (Newton second)

Impulse

What is impulse?

It is the change in momentum.

Large impulse

Equations for Impulse

Two ways to determine impulse.

Dp = mDv

change of momentum = mass x change in velocity

Or

Dp = FDt

change of momentum = force x change in time

Example of impulse

A 10 kg object change velocity from 3 m/s to 10 m/s has an impulse of

impulse Dp = 10 * (10 – 3)

= 70 Ns

Some Examples

A 100Kg man is running at 5.6m/s. What is his momentum?

Some Examples

A 100Kg man is running at 5.6m/s. What is his momentum?

p = 100 * 5.6 = 560 Ns (600 Ns)

Some Examples

How fast is a 1.50 kg ball moving if it has a momentum of 4.50 kg·m/s?

Some Examples

How fast is a 1.50 kg ball moving if it has a momentum of 4.50 kg·m/s?

p = mv

4.50 Ns = 1.50 kg * v

v = 4.50/1.50 = 3.00 m/s

Some Examples

A net force of 100 Newton’s is applied to a wagon for 5 seconds. This causes the wagon to undergo an impulse of?

Some Examples

A net force of 100 Newton’s is applied to a wagon for 5 seconds. This causes the wagon to undergo an impulse of?

Dp = FDt

Dp = 100 * 5 = 500 Ns

How?