1. Forces

2. What Is a Force? Force- a push or a pull that acts on an object
Can cause a resting object to move, or it can accelerate a moving object
Forces are measured in Newtons (N)
One newton is the forces that causes 1 kg mass to accelerate at a rate of 1 meter per second each second
1 N = 1 kg*m/s2

3. Representing Force
Forces can’t be seen, but their effects can. So we have come up with a way to represent forces

4. Forces can be combined Forces in the same direction add together
Forces in opposite directions subtract from one another
The net force is the overall force acting on an object after the forces are combined

5. Balanced and Unbalanced Forces
When forces on an object are balanced, the net force in zero and there is no change in the object’s motion
When an unbalanced force acts on an object, the object accelerates

6. Friction
A force that opposes the motion of objects that touch as they move past each other
4 main types of friction:
1.) static friction
2.) sliding friction
3.) Rolling friction
4.) fluid friction

7. Static Friction Acts on object that are not moving
Always acts in the direction opposite to that of the applied force
You experience static friction every time you take a step

8. Sliding Friction
Force that opposes the direction of motion of an object as it slides over a surface
- Less than static friction. Therefore, less force is needed to keep an object moving than to start it moving

9. Rolling Friction Friction force that acts on rolling objects
100 to 1000 times less than the force of static or sliding friction
Helps explain why professional movers use wheeled dollies to move heavy objects

10. Fluid Friction Opposes the motion of an object through a fluid
Examples can be seen on a submarine moving through water or an airplane flying through air
You can feel fluid friction when stirring thick cake batter
Increases as the speed of the object moving through the fluid increases
Fluid friction acting on an object moving through the air is known as air resistance

11. Gravity Force that acts between any 2 masses
-attractive force—pulls objects together
-does not require objects to be in contact
-can act over long distances
-Earth’s gravity acts downward toward the center of Earth

12. Falling Objects
Gravity causes objects to accelerate downward, whereas air resistance acts in the direction opposite to the motion and reduces acceleration

13. Falling objects
As objects fall to the ground, they accelerate and gain speed
Terminal velocity is the constant velocity of a falling object when the force air resistance equals the force of gravity
-the doesn’t mean the objects stop in mid air…it just means it doesn’t accelerate anymore
Mass does NOT matter, all objects fall at the same rate

14. Projectile Motion
The motion of a falling object (projectile) after it is given an initial forward velocity.
Air resistance and gravity are the only forces acting on a projectile