1. Section 1-1
The Nature of Force

2. Observing Motion by Using a Reference Point
Motion- a change in position of an object over time relative to a reference point
Reference Point- object that appears to stay in place
Common Reference Points
Earth
Trees
Buildings

3. Speed
Speed- the distance traveled by an object divided by the time taken to travel that distance
SI unit for speed is m/s
Formula for speed
Average Speed= total distance/total time
Speed is shown on a graph as distance versus time

4. Velocity: Direction Matters
Velocity- speed of an object in a particular direction
Difference between speed and velocity is direction
Velocity will change either when speed or direction changes
Combining Velocity
Velocities moving in the same direction are added
Velocities moving in opposite directions are subtracted

5. Acceleration Acceleration- rate at which velocity changes
Increase of acceleration- positive acceleration
Decrease of acceleration- negative acceleration or deceleration
Faster the velocity change, the greater the acceleration
Average acceleration= final Velocity – starting velocity/time

6. Acceleration on a graph
Shown on a graph as velocity versus time

7. Circular Motion: Continuous Acceleration
Objects traveling in circular motion are always changing its direction
Therefore, velocity is always changing, so it is accelerating
Centripetal Acceleration- acceleration that occurs in a circular motion

8. Force A force is a push or pull
All forces have both size and direction
The SI unit of force is the newton (N)
The more newtons, the greater the force

9. Forces Act on Objects
All forces are exerted by one object on another object
One object exerts a force as another receives a force
However, just because a force is being exerted by one object on another doesn’t mean that motion will occur

10. Determining Net Forces
Net force- combining all the forces acting on an object
Forces in the Same Direction- add the forces together to determine the net force.
Forces in Different Directions- subtract the smaller force from the larger force to determine the net force

11. Unbalanced Forces Produce a Change in Motion
When the net force on an object is not zero, the forces on the object are unbalanced
Unbalanced forces produce a change in motion
Unbalanced forces are necessary to cause a nonmoving object to start moving or change the motion of moving objects
An object can continue to move even when the unbalanced forces are removed

12. Balanced Forces Produce No Change in Motion
When the forces applied to an object produce a net force of zero, the forces are balanced
Balanced forces do not cause a nonmoving object to start moving
Balanced forces will not cause a change in the motion of a moving object