Chapter 12.1 Momentum.

Presentation on theme: "Chapter 12.1 Momentum."— Presentation transcript:

1 Chapter 12.1 Momentum

2 Depends on both mass and velocity
Momentum A property of moving mass that resists changes in a moving object’s velocity vector (speed or direction) Depends on both mass and velocity

3 Momentum The symbol for momentum is lower case p with an arrow on top. The arrow signifies that momentum is a vector.

4 Remember! Velocity, by definition, is negative to the left.
Velocity is positive to the right.

5 Momentum depends upon velocity
Momentum is positive when to the right, again by definition. Momentum is negative to the left. Left and Right depend upon your frame of reference.

6 FΔt = Δp FΔt=m(vf – vi) F=Δp/Δt Impulse So, what?
The yellow part is called impulse. The blue part is called change in momentum. FΔt=m(vf – vi) F=Δp/Δt So, what?

7 Which object is more difficult to stop if both are traveling at the same speed?
Why?

8 FΔt = Δp vs. FΔt=Δp Let’s look at this concept another way…
Impulse The bowling ball is more difficult to stop because bringing it to a stop depends upon velocity and mass. More massive objects require more energy to have their motion changed. These changes occur by applying forces to the object(s). The more time a force is applied, the larger the change in motion. If the force is only applied for a small time, the change in motion is less. FΔt = Δp vs. FΔt=Δp Let’s look at this concept another way…

9 How do things change if we hold Δp constant and vary the time?
Impulse How do things change if we hold Δp constant and vary the time? As the time decreases, and change in momentum remains the same, then the force will increase. Think about bringing a car to a stop in a very short time… how hard must the brakes be applied? (i.e. how large is the force?) The take-home point: a change in momentum over a large amount of time requires a smaller force and is often safer/less damaging. And a change in momentum over a short time requires a large force which can be damaging or even fatal. Watch this video for more good stuff: Understanding Car Crashes

10 Occurs when two or more objects hit each other.
Collision Occurs when two or more objects hit each other. Momentum is transferred from one object to another.

11 Physics in Action Figuring out what will happen or what has happened in a collision is tricky business because many of Newton’s Laws need to be used. Take a look at these pictures and see if you can spot inertia, impulse, momentum and some collisions.

12 Law of Conservation of Momentum
For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. That is, the momentum lost by object 1 is equal to the momentum gained by object 2. (physicsclassroom.com)

13 Momentum Conservation
This is a specific type of collision is which one object is initially at rest and then the other object is at rest after the collision. “Momentum gained by object 2 from object 1” does not mean it has the velocity that object one did. Why? Because momentum depends on ________ and _________.

14 Elastic Collision Occurs when objects bounce off each other with no loss in the total kinetic energy. 𝐾𝐸 𝑖 = 𝐾𝐸 𝑓

15 Inelastic Collision The system loses kinetic energy as objects change shape (deform) or energy transforms to heat (via friction), or sound. Most collisions in everyday life fall into this category.

16 Perfectly Inelastic Collision
Perfectly inelastic collisions are defined as a collision in which two separate objects stick together, and travel together after impact. Again, total KE of the system decreases.