Chapter 12: Forces & Motion
12.1 (pg’s 356-362)Forces
- Force: can cause a resting object to move, or it can accelerate a moving object by changing the object’s speed or direction.
- Force is measured in newtons (N). 1 N is the force that cause a 1-kg mass to accelerate at a rate of 1 meter per second each second (1N = 1kg x m/s2 )
- A Newton (N) a unit of force, explains how force, mass, and acceleration are related.
- Representing Force: an arrow to represent the direction and strength of force.
- Combining Forces:
- Net Force: the overall force acting on an object after all the forces are combined.
- Forces in the same direction add together
- Forces in opposite directions subtract from one another.
- Balanced Forces: when the forces on an object are balanced, the net force is zero and there is no change in the object’s motion.
- Unbalanced Forces: an unbalanced force acts on an object, the object accelerates.
- Friction: a force that opposes the motion of objects that touch as they move past each other.
- Static Friction: force that acts on objects that are not moving.
- Sliding Friction: force that opposes the direction of motion of an object as it slides over a surface.
- Rolling Friction: force that act on rolling objects.
- Fluid Friction: force that opposes the motion of an object through a fluid.
- Gravity: is a force that acts between any 2 masses.
- Gravity is an attractive force that pulls object together.
- Earth’s gravitational force exerts a force of attraction on every other object that is near Earth.
- The force of gravity does not require objects to be in contact for it to act on them.
- Earth’s gravity act downward toward the center of Earth.
- An upward force or supporting force balances the fownward force of gravity.
- Falling Objects: Gravity causes objects to accelerate downward, where as air resistance acts in the direction opposite to the motion and reduces acceleration.
12.2 (pg’s 363-371) Newton’s First & Second Laws of Motion:
- 1st Law: the state of motion of an object does not change as long as the net force acting on the object is zero.
- Sometimes called the Law of Inertia: the tendency of an object to resist a change in its motion.
- An object at rest tends to remain at rest, and an object in motion tends to remain in motion with the same direction and speed.
- 2nd Law: The acceleration of an object is equal to the force acting on it divided by the object’s mass.
- Doubling the mass of an object cuts its acceleration in half.
- The acceleraion of an object is always in the same direction as the net force.
- Mass & Weight:
- Mass is a measure of the inertia of an object, how much “stuff” something is made up of.
- Weight is a measure of the force of gravity acting on an object.
12.3 (pgs. 372-377) Newton’s Third Law of Motion & Momentum
- Newton’s 3rd Law: whenever on object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. (action and reaction forces)
- Momentum: is the product of an object’s mass and its velocity.
- An object has a large momentum if the product of its mass and velocity is large.
- Conservation of Momentum: if not net force acts on a system, then the total momentum of the system does not change.
- Closed system: other objects and forces cannot enter or leave a system.
- In a close system, the loss of momentum of one object equals the gain in momentum of another object, momentum is conserved.
12.4 (pgs. 378-382) Universal Forces:
- Electromagnetic Forces: are associated with charged particles
- Nuclear Forces: the strong nuclear force and the weak nuclear force, act within the nucleus to hold it together
- Gravitational Force: every object in the universe attracts every other object.
- It takes a huge mass such as Earth’s to exert a large gravitational force.
- Gravity is the weakest universal force, but it is the most effective over long distances.