Forces and Collisions
What is force?
Force is a push or pull that acts on an object.
If a person slaps someone else's face with 12 Newtons of force, how much force is the hand experiencing from the face?
12 Newtons (Newton's 3rd law!)
What causes an object to change in motion?
Energy transfer
Draw 2 free body diagrams showing the forces acting on a collision between 2 cars
Diagram 1: car 1 with a force arrow that is labeled "force from car 2"
Diagram 2: car 2 with a force arrow (same in size, opposite direction) that is labeled "force from car 1"
What is the unit for measuring force?
Newtons
If a ball hits the floor with 4 Newtons of force, what is the force of the floor on the ball?
4 Newtons (always equal!)
How are kinetic and potential energy different?
Kinetic energy is energy of motion (ex: a ball rolling) vs. potential energy is stored energy (ex: a compressed spring). These two forms of energy can transfer between each other.
Draw 2 free body diagrams showing the forces acting on a face and hand when the two collide
Diagram 1: face with a force arrow that is labeled "hand force"
Diagram 2: face with a force arrow (same in size, opposite direction) that is labeled "face force"
What is involved in a collision?
Two objects hitting each other--at least one of the objects must be moving
What is a peak force?
The maximum force an object experiences during a given collision
A ball is flying through the air at 50 kph. How could you make it have more kinetic energy?
Throw it faster
Its breaking point
What causes an object to change shape?
Force
Regardless of the collision, what can you say about the peak forces acting on the two objects involved?
In every collision, the peak force on the first object would be the same as the peak force on the other object in the collision = Newton's 3rd law of motion!
Kinetic energy depends on both mass and speed. Will mass or speed make a bigger difference in the amount of KE?
Speed, because it is a squaring effect. 3 times as much speed = 9 times as much energy.
Whereas mass is linear: 3 times as much speed = 3 times as much energy
A collision whose objects reach their breaking points results in permanent deformation/damage. What factors could be changed to reduce damage?
Less mass
Less speed
What is Newton's 3rd law?
His 3rd law states that when one object exerts force on a second object, the second object exerts a force on the first. These forces are equal in strength and opposite in direction.
How does peak force relate to kinetic energy?
Peak force depends on kinetic energy. The more kinetic energy (mass and speed), the more peak force involved.
You have 3 ddifferent collisions:
1. Two volleyball players running into each other
2. A volleyball player returning a served ball
3. A volleyball player hitting her head on the ground
Which collision has the LEAST kinetic energy involved and why?
The third collision, because KE depends on speed and mass. Because the ground is not moving, it has zero KE.