1. FORCES
Chapter 3

2. Force, mass and acceleration
The greater the force on an object, the greater the objects acceleration
The acceleration depends on its mass as well as the force exerted on it.

3. Newton’s second law of Motion
The acceleration of an object is in the same direction as the net force on the object
Acceleration= net force(in Newtons)
Mass (in Kilograms)
A=F m
If the mass of a helicopter is 4.500kg and the net force on it is 18,000N. What is the helicopters acceleration?
A car is being pulled by a tow truck. What is the cars mass if the net force on the car is 3,000N and it has an acceleration of 2.0m/s?

4. Friction
Friction is the force that opposes motion between the two surfaces that are touching each other.
Friction depend on the types of surfaces and the force pressing the surfaces together
Friction results from the microwelds formed between the two surfaces that are in contact

5. Friction
static friction- caused by microwelds-the force that opposes the motion of two surfaces sliding past each other
Sliding friction- caused by microwelds- the friction formed by microwelds formed between two surfaces
Rolling friction- the frictional force between a rolling object and the surface it is rolling on.

6. Air resistance
Air resistance is the force that acts on objects moving through the air
For example: an open parachute
The amount of resistance depends on the speed, size and shape of the object.

7. GRAVITY
The attractive force between ant two objects that depends on the masses of the objects and the distance between them.
If the mass increases- the gravitational force increases
If the objects are closer together- the gravitational force increases

8. The law of Universal Gravitation
The gravitational force between two objects depends on the masses of the objects and the distance between them
Gravitational force= (constant) X (mass1)x (mass2) distance
The acceleration to gravity near Earths surface is 9.8m/s2
Near Earth’s surface the gravitational force on an object with mass,m, is given by:
F=mg

9. Weightlessness and freefall
an object in orbit seems to be weightless because it is falling around Earth Ex. Floating in space, space shuttle
Projectile motion
Earths gravity causes projectiles to follow a curved path because their horizontal motion is constant, but gravity causes the vertical motion to be changing. EX. A thrown ball
Centripetal Force
The net force on an object moving in a circular path. Ex. A car on a curved highway, the swing ride at an amusement park

10. Newton’s third Law of Motion
Describes action-reaction pairs this way: When one object exerts force ona second object, the second one exerts a force on the first that is equalin strengthand opposite in direction.
- action –reaction- a force is applied in nature, an equal force is applied. Ex. Trampoline, figure skaters, rocket propulsion

11. Momentum
A property of a moving object that states how much force is needed to change its motion .
Momentum( kg m/s)= mass 9kg) X velocity (m/s)
P=mv
What is the momentum of a car with a mass of 1,300kg traveling at a speed of 28m/s?
What is the mass of a person walking at a speed of 0.8 m/s if their momentum is 52 kg.m/s?

12. momentum

13. Law of Conservation of Momentum
If objects exerts forces only on each other, their total momentum is conserved
In a collision, momentum is transferred from one object to another.