Velocity Review

• 1. What is the difference between speed and velocity?

• 2. Write down an example of speed and an example of velocity.

Even More Practice

• A plane is flying from Atlanta to San Diego at 520 mph west. It encounters wind from the jet stream moving at 30 mph east. What is the planes resultant velocity?

• What about if the plane were headed east from San Diego to Atlanta instead?

Bellringer

• Give an example of an object in freefall.

3.3 Acceleration and direction• Remember..a change in velocity occurs

whenever there is a change in speed, direction, or both.

3.3 Acceleration• Acceleration is the rate at which

velocity changes. (How quickly an object changes speed or direction)

3.3 Speed and acceleration

• Speed and acceleration are not the same thing.

• Acceleration is the change in speed divided by the change in time.

Acceleration Calculations

If you start from a standstill and are going 5 meters per second at the end of 5 seconds, what is your rate of acceleration?

Explain why each of the following is an example of

acceleration….

• A plane taking off• Stopping at a

corner• Jogging on a

track• Driving around a

corner

• Increase in speed• Decrease in

speed• Change in

direction• Change in

direction

3.3 Acceleration and motion graphs• A speed vs. time

graph is useful for showing how the speed of a moving object changes over time.

• If the line on the graph is horizontal, then the car is moving at a constant speed. There is no change in speed

so there is no acceleration.

3.3 Acceleration and motion graphs

• Like velocity, acceleration can be positive or negative.

• Positive acceleration adds more speed each second.

Speed is increasing at the same rate.

3.3 Acceleration and motion graphs

• Negative acceleration subtracts some speed each second, so things get slower.

• People sometimes use the word deceleration to describe slowing down.

Speed is decreasing at the same rate.

Graphing Acceleration

• Between which 2 points do you find:

1. Negative acceleration?

2. Positive acceleration?

3. Steady speed?

Try this one…

• A coconut falls from the top of a tree and reaches a velocity of 19.6 m/s when it hits the ground. It takes 2 seconds to reach the ground. What is the coconut’s acceleration?

(remember to include units and direction in your answer)

Solution

• a = (v2-v1) =

t

What force is causing the coconut to fall downward?

Solution

• a = (v2-v1) =

t

What force is causing the coconut to fall downward?

GRAVITY

3.3 Free fall

• An object is in free fall if it is accelerating due to the force of gravity and no other forces are acting on it.

• Objects in free fall on Earth accelerate downward.

3.3 Free fall• Falling objects increase their speed by 9.8

m/s every second, or 9.8 m/s2 • The letter “g” is used for acceleration due to

gravity.

3.3 Acceleration and direction• Acceleration occurs whenever there is a

change in speed, direction, or both.

3.3 Acceleration and direction• A car driving around a curve at a

constant speed is accelerating because its direction is changing.

3.3 Curved motion

• A soccer ball is an example of a projectile.

• A projectile is an object that is moving forward AND is also under the influence of gravity.

3.3 Curved motion

• Circular motion is another type of curved motion.

• An object in circular motion has a velocity vector that constantly changes direction.

Section Review – page 73

• 3, 4, 5• 7, 8, 9