1. Acceleration & Force
Section 8.2

2. Acceleration
Acceleration = change in velocity divided by the time interval in which the change occurred.
Equation:
Acceleration = final velocity - initial velocity
time
a = ∆v m
t s2
Unit=

3. Graphing Acceleration
To graph acceleration:
Plot velocity on the y - axis
Plot time on the x - axis v v v t t t
Traveling at constant
velocity; a = 0 m/s2
a is increasing
(+)
a is decreasing
(-)

4. Force
When a force is exerted on an object it causes an acceleration, or change in an object’s velocity
Usually a combination of forces act on an object at any given time (net force)
An object accelerates in the direction of the net force.

6. Balanced/Unbalanced Forces
Balanced forces: forces cancel each other out. Net force= zero so there is NO movement.
Unbalanced forces: forces acting on an object produce a nonzero net force
Acceleration of an object is in the direction of the greater force.
Therefore movement occurs.

7. Here is an example of balanced forces
Here is an example of balanced forces. There is no movement by either object.
Figures a, b, and c are all examples of unbalanced forces because there is change in motion.

8. Friction
The force between two objects in contact that opposes the motion of either object.
Frictional force will vary according to surfaces
rough - rough smooth – smooth
 frictional  frictional
force forces

9. Air Resistance Form of friction…
Air resistance = the interaction between surface of an object in motion and air molecules.
Depends on size, shape, and speed of the object.
Lots of air resistance
Not a lot of
air resistance
(aerodynamic)

10. Gravity
defined as the attraction between two particles of matter due to their mass
Gravity occurs between all objects
Acts on objects even when they do not touch
Depends upon mass and distance
 mass,  force of  distance,  force of
gravity gravity

11. Look mom, no gravity!

12. Now I’m Freeeeee, Free Falling… -Tom Petty
Free Fall = the motion of a body when only the force of gravity is acting on it
free fall acceleration = g (force of gravity)
g = 9.8 m/s2 near earth’s surface
Weight = force on an object due to gravity
w = mg where g is equal to 9.8 m/s2
Weight is a force so its unit is N

13. Relationship between velocity/ air resistance/weight
When the force of air resistance becomes equal to the gravitational force on an object, the object stops accelerating & reaches maximum velocity or terminal velocity.

14. Notice, as the weight of the person increases so does the air resistance and the force of gravity on that person’s mass