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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
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