Unit 19 - Forces And Motion
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Transcript of Unit 19 - Forces And Motion
![Page 1: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/1.jpg)
Forces and Motion
Unit 19
![Page 2: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/2.jpg)
What words can you think of to describe the motion of an
object?
![Page 3: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/3.jpg)
VELOCITY
The word scientists use to describe how fast an object is moving in a
certain direction.
![Page 4: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/4.jpg)
Velocity is measured as:
change in distance
change in time
a change in distance per change in time
What are some things you can think of that are measured like this?
![Page 5: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/5.jpg)
What are some examples of objects that move at high
velocities?
1600 mph
220 mph
![Page 6: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/6.jpg)
Extreme Velocities
17,000 mph 40,000 mph
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What are some examples of low velocities?
50 yds/hr (.03 mph)
1.2 mph
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What units would you use to measure the velocity of an object moving in this classroom?
meters per second
m
s
Meters per second tells us how many meters something can move in one second.
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Converting Velocities
m/s into km/hr
m
s
Just take the m/s multiply by 1000 and divide by 3600
1000 m/km
3600 seconds/hr
“What kind of mileage does this get?”
![Page 10: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/10.jpg)
Converting Velocities
m/s into km/hr
m
s
Just take the m/s multiply by 1000 and divide by 3600
1000 m/km
3600 seconds/hr
“What kind of mileage does this get?”
1 hwy, 0 city1 highway, 0 city
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What else can we know about an object’s motion besides velocity?
• What if the object slows down?
What if the object’s velocity changes?
• What if the object speeds up?
![Page 12: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/12.jpg)
Scientists have a special way to measure a change in
velocity:
Acceleration
Acceleration is a change in velocity.
![Page 13: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/13.jpg)
Visualizing Acceleration
• Here you can see how the ball travels a further and further distance each second.
• That is because its velocity is continuing to increase.
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• If you’re speeding up, you have positive acceleration.
• If you’re slowing down, you have negative acceleration.
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Example:You’re driving along in your car and
suddenly have to slam on your brakes for a red light.
Negative or positive acceleration?
High or low acceleration?
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Answers
• Negative Acceleration• High Rate
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You’re an astronaut waiting in your shuttle for takeoff. Suddenly the rockets fire and you’re on your way.
High or low positive or negative acceleration?
Example:
![Page 18: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/18.jpg)
Or you are a drag racer
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Answer
High positive acceleration because you’re speeding up quickly.
![Page 20: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/20.jpg)
You’re driving down the highway when your car runs out of gas and you slowly roll to a stop on the side of the road.
Example:
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Answer Low negative acceleration because you’re slowing down slowly.
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Example:• You are at cruising speed on the highway.
You no longer feel any pressure against the seat or are lurching forward.
• What is your acceleration?
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Answer Zero, because you are at constant velocity
That velocity can be fast, slow, or not moving at all.
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Challenge Question:
You throw a basketball up in the air. It rises to a certain height and then falls back to earth.
Describe its acceleration
Hint: There are multiple steps
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Answer
First, high positive acceleration because it speeds up quickly as it leaves your hand.
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Answer
Then, as it rises, low negative acceleration, because it begins to slow down slowly because of gravity.
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Answer
At the top of the arch, it has zero acceleration, because it briefly stops moving upward and has constant velocity.
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Answer As it begins to fall again, low positive acceleration, because it speeds up slowly.
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Answer
Finally, when you catch it, high negative acceleration because it slows down very quickly in your hand.
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How Do I Graph the Motion of a Particle?
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5
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20
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Car 1 Car 2 Car 3
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Car 1 is moving with a velocity of 1 m / sec
There is zero acceleration
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Car 1 Car 2 Car 3
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Car 2 has constant velocity throughout at 1 m /sec
Its acceleration remains zero
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15
20
25
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Car 1 Car 2 Car 3
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Car 3 has a changing velocity throughout, finishing at 7 m / sec
Acceleration is 1 m / sec2
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Car 1 Car 2 Car 3
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Quick Review
• Velocity: speed of motion in a direction
• Acceleration: change in velocity
What causes an object’s velocity to change?
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• If you’re riding your bike and want to speed up, what do you do?
• If you’re driving a car and want to slow down, what do you do?
• If you’re playing soccer and want to move the ball,
what do you do?
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Nothing will change speed unless acted upon by a force.
If it’s sitting still, it will keep sitting still.
If it’s moving fast, it will keep moving fast.
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• That force can act to accelerate it
Only a force can change the velocity of an object.
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• That force can act to decelerate it
Only a force can change the velocity of an object.
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Then why do things slow down?
• Flying balls slow down and eventually stop because of the force of gravity.
• Cars and bikes eventually slow down and stop because of the force of friction.
![Page 40: Unit 19 - Forces And Motion](https://reader035.fdocuments.us/reader035/viewer/2022062419/55865d1cd8b42a23108b462c/html5/thumbnails/40.jpg)
Then why do things slow down?
• In space with no friction and no gravity, objects will keep going at the same speed forever without a force to slow them down or speed them up.