Unit 2 Lesson 5: Momentum & Energy

• Describe the relationship between Mass and Velocity

• Relate the impulse on a body to the resulting change in momentum

  • Relate when momentum is and is not conserved

What is Momentum?

• Momentum is Inertia in Motion

  • Larger objects are harder to stop than smaller ones

• Equations

  • We use p as the variable for momentum so we don't confuse it with mass​

    • When direction matters: p=m*v

    • When direction does not matter: p=m*s

• The more momentum something has, the more difficult it is to stop, and the larger the effect it will have in a collision

Calculating Momentum Sample Problem 1

• Calculate the momentum of a 10 kg bowling ball rolling at 3 m/s

  • Step 1: Identify your Variables

    • m= 10 kg

    • V= 3 m/s

    • p=?

  • Step 2: Plug your variables into your equation and solve

    • p= 10 × 3

Calculating Momentum Sample Problem 2

• A school bus traveling at 11.1m/s has a momentum of 152625 kg.m/s. What is the mass of the bus?

  • Step 1: Identify your Variables

    • m= ? kg

    • V= 11.1 m/2

    • p=

  • Step 2: Plug your variables into your equation and solve

    • 152625= m × 11.1

Changes in Momentum

• For momentum to change, there needs to be either a change in mass or velocity

  • Most of the time, it is the velocity that changes

    • ​Acceleration results from a force

      • A Greater force = A greater change in velocity and a greater change in momentum

Momentum and Time

• Time also affects Momentum

  • If you exert the same force over a longer period, a greater change in momentum

  • A long-sustained force produces more change in momentum than the same force applied breifly

Increasing Momentum

• If you want to have the maximum increase in momentum, you apply the greatest force and extend the time

  • Example: think of a long form canon

    • The force of momentum is greater in longer barrels because the force force of gun powder is applied over a longer period of time

      • The force does slowly decrease over time

Energy

• Energy: the ability to do work

  • Measured in the Unit joules

  • two main types of energy

    • Potential energy

    • Kinetic energy​

• Energy is neither lost nor gained within a system, but changes from one form of energy to another

Potential energy

• Potential energy is energy stored due to the position of the object

  • Energy that is not yet in motion

    • ​Example: think of a bow and arrow, as the archer pulls the bow back, the arrow is not yet moving, but has the potential to do so once released

    • Example 2: Picture a car at the top of a hill just before it goes down.

Gravitational Potential energy

• Gravitational Potential Energy: energy an object has due to being elevated

  • Is equal to the amount of work done against gravity

    • GPE= Force x height

    • GPE= mass x gravity x height​

  • Depends only on the distance to the ground, not necessarily the path to get there

Kinetic Energy

• Kinetic Energy: The energy of an object due to its motion

  • Can be transferred from one object to another

• Depends on the mass and speed of the object

  • Can only be a positive number

Kinetic Energy Sample Problem 1

• Calculate the Kinetic Energy of a 1-kg Parrot flying at 6 m/s.

  • Step 1: Identify your variables

    • m= 1 kg

    • v = 6 m/s

  • Step 2: Plug your variables into your equation and solve