Why is this teacher having all the fun?

In this lesson, you will look at the Interactive popup. Assistance may be required. law of conservation of momentum.

Law of Conservation of Momentum
In a closed isolated system, total mechanical energy is conserved

System: Group of related objects
Closed: No mass enters or leaves the system
Isolated: No unbalanced outside forces—no work done on the system
Conserved: Stays the same
Momentum: A measure that quantifies (puts a number to) motion → p = mv

p_1i + p_2i = p_1f + p_2f
m₁v_1i + m₂v_2i = m₁v_1f + m₂v_2f

In the equation, there are 2 objects m₁ and m₂ that are the masses of each and v₁ and v₂ are the velocities of each, also the subscript i means initial and the subscript f means final.

The most common conservation of momentum problems are collisions and explosions. These are situations where momentum is transferred from one object to another, but the total for the system stays the same.

For example, a rocket works by the principle of conservation of momentum. A rocket sitting on the launch pad has zero momentum. When the rocket engines ignite, hot gasses come shooting out one end of the rocket at an incredibly high velocity. This gas has momentum down. In order for momentum to be conserved, the rest of the system (the rocket) has to gain an equal momentum up.

Source: Apollo Rocket Launch, NASA, Wikimedia Commons

Investigating the Law of Conservation of Momentum

Watch the two videos below. Each video provides information about the law of conservation of momentum in different ways.

Video 1

Video 2

In your notes, answer the following questions using the information from the videos:

1. What is the law of conservation of momentum?

   Interactive popup. Assistance may be required.

   Check Your Answer

   If an object is propelled by another object, the first object will transfer its momentum to the second object.

2. How do you calculate the law of conservation of momentum?

   Interactive popup. Assistance may be required.

   Check Your Answer

   M_i (Mass initial) × V_i (Velocity initial) = M_f (Mass final) × V_f (Velocity final)

3. What are some examples of the law of conservation of momentum from the video and from your own understanding?

   Interactive popup. Assistance may be required.

   Check Your Answer

   A few possible examples are a ball hitting another ball on a pool table, Newton’s cradle, and a baseball bat hitting a baseball.

4. What happens when an object with a small mass is propelled toward an object with a large mass?

   Interactive popup. Assistance may be required.

   Check Your Answer

   The small object transfers it’s momentum to the object with the large mass, but the object with the large mass moves slowly.