Newton's Laws and Momentum

Action and Reaction Pairs

1 force is called the action force, and the other is called the reaction force. While balanced forces are equal and opposite too, action/reaction forces act on different objects, while balanced forces only act on 1 object.

Momentum

A measure of mass in motion. The momentum of an object is a product of its mass and velocity. (Momentum= mass x velocity, p=mv) The unit for momentum is kg x ms

Force

A push or pull

Collision

A sitiuation in which two objects in close contact exchange energy and momentum.

Forces on Moving Objects

An object with forces acting on it can be moving at a constant velocity as long as the forces are balanced. Ex. Riding a bike down a straight line at a constant speed= balanced forces.

Centripetal Force

Any force that keeps an object moving in a circle. The direction of this force points towards the center of the circle, and without this force, the object would go flying out in a straight line. If the size of the centripetal force is known, the acceleration can be found (w/ Newton's 2nd Law). A greater acceleration requires a greater centipetal force.

Balanced Force

Can't change an object's speed or direction.

Types of Forces

Contact Force- when one object pushes or pulls another object by touching it. (The 1st object is applying contact force to the 2nd) Gravity- the force of attraction between to objects because of their masses. Friction- a force that resists the motion between 2 surfaces in contact.

Force Formulas

Force- f=ma Mass- m= f/a Acceleration- a= f/m

Unbalanced Force

Is needed to change an object's motion.

Momentum and Newton's 3rd Law

Momentum is conserved whenever the only forces acting on the objects are action/reaction pairs.

Momentum Formulas

Momentum- p=mv Mass- m= p/d Velocity- v= p/m

Types of Collisions (1st Type)

Objects bounce off each other. Most of the force goes into changing the motion of the objects, making them travel back seperately. The combined momentum of the objects after the collision is the same as it was before it.

Types of Collisions (2nd Type)

Objects stick and move together. The total momentum of the objects is conserved after the collision. After the collision, the 2 objects move together w/ a combined momentum equal to the 1st object before the crash. The 1st object has a certain momentum, & the 2nd object has no momentum. Ex. In a car crash, momentum is conserved, but some energy goes into the bending of the cars.

Net Force

Overall force acting on an object when all the forces are combined. If the forces are balanced, its net force is zero.

Newton's Third Law

States that every time an object exerts a force on another object, the second object exerts a force that is equal in size and opposite in direction back on the first object. (Action and Reaction)

Newton's First Law

States that objects at rest stay at rest, and object's in motion stay in motion remain in motion with the same velocity, unless acted upon by an unbalanced force. (Also called law of inertia)

Newton's Second Law

States that the acceleration of an object increases with an increased force and decreased with increased mass. (Force= mass x acceleration, F=ma)

Conservation of Momentum

States that the total momentum of a system of objects does not change, as long as no outside forces are acting on that system.

Momentum Can Be Transfered

The object with the less mass will have a greater change in velocity if the two objects in the collision have very different masses.

Inertia

The resistance of an object to a change in its speed or direction of its motion. Closely related to mass; inertia is measured when you measure an object's mass.

Finding the Momentum of Objects

To find the total momentum of a system of objects before a collision, combine the momentum of both objects. (Works for objects going in the same direction) For objects going in different directions, suntract the momentum of one object from the other. This will get the final momentum (use the principle of conservation of momentum)

Momentum is Conserved

When 2 objects collide. the velocity and momentum of each object change, but the total momentum of both objects does not change (because there are no outside forces acting on them). The amount an object's momentum changes depends on the size of the force and how long its applied for; think Newton's 3rd Law.