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Force and motion
This document discusses forces and motion. It defines key terms like velocity, acceleration, and force. Velocity is how fast an object is moving in a direction, measured in meters per second. Acceleration is a change in velocity caused by an applied force and can be positive (speeding up) or negative (slowing down). Forces like gravity and friction are what cause changes in an object's motion by speeding it up or slowing it down. Graphs are used to visualize changes in position, velocity, and acceleration over time.
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Force and motion
- 1. Forces and Motion Unit 19
- 2. What words canyou think of to describe the motion of an object?
- 3. VELOCITY The word scientistsuse to describe how fast an object is moving in a certain direction.
- 4. Velocity is measuredas: a change in distance per change in time change in distance change in time What are some things you can think of that are measured like this?
- 5. What are someexamples of objects that move at high velocities? 220 mph 1600 mph
- 6. Extreme Velocities 17,000 mph 40,000 mph
- 7. What are someexamples of low velocities? 50 yds/hr (.03 mph) 1.2 mph
- 8. What units wouldyou 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.
- 9. 11 hwy, 0city highway, 0 city Converting Velocities m/s into km/hr “What kind of mileage does this get?” m 1000 m/km s 3600 seconds/hr Just take the m/s multiply by 1000 and divide by 3600
- 10.
- 11. What else canwe know about an object’s motion besides velocity? •What if the object speeds up? • What if the object slows down? What if the object’s velocity changes?
- 12. Scientists have aspecial way to measure a change in velocity: Acceleration Acceleration is a change in velocity.
- 13. Visualizing Acceleration • Hereyou can see how the ball travels a further and further distance each second. • That is because its velocity is continuing to increase.
- 14. • If you’respeeding up, you have positive acceleration. • If you’re slowing down, you have negative acceleration.
- 15. Example: You’re driving alongin your car and suddenly have to slam on your brakes for a red light. Negative or positive acceleration? High or low acceleration?
- 16. Answers • Negative Acceleration •High Rate
- 17. Example: You’re an astronautwaiting in your shuttle for takeoff. Suddenly the rockets fire and you’re on your way. High or low positive or negative acceleration?
- 18. Or you area drag racer
- 19. Answer High positive accelerationbecause you’re speeding up quickly.
- 20. Example: You’re driving downthe highway when your car runs out of gas and you slowly roll to a stop on the side of the road.
- 21. Answer Low negative accelerationbecause you’re slowing down slowly.
- 22. Example: • You areat cruising speed on the highway. You no longer feel any pressure against the seat or are lurching forward. • What is your acceleration?
- 23. Answer Zero, because youare at constant velocity That velocity can be fast, slow, or not moving at all.
- 24. 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
- 25. Answer First, high positiveacceleration because it speeds up quickly as it leaves your hand.
- 26. Answer Then, as itrises, low negative acceleration, because it begins to slow down slowly because of gravity.
- 27. Answer At the topof the arch, it has zero acceleration, because it briefly stops moving upward and has constant velocity.
- 28. Answer As it beginsto fall again, low positive acceleration, because it speeds up slowly.
- 29. Answer Finally, when youcatch it, high negative acceleration because it slows down very quickly in your hand.
- 30. How Do IGraph the Motion of a Particle? 30 Car 1 Car 2 Car 3 25 20 15 10 5 0 0 1 2 3 4 5 6 7
- 31. 30 Car 1 Car 2 Car 3 25 20 15 10 5 0 0 1 2 3 4 5 6 7 Car 1 is moving with a velocity of 1 m / sec There is zero acceleration
- 32. 30 Car 1 Car 2 Car 3 25 20 15 10 5 0 0 1 2 3 4 5 6 7 Car 2 has constant velocity throughout at 1 m /sec Its acceleration remains zero
- 33. 30 Car 1 Car 2 Car 3 25 20 15 10 5 0 0 1 2 3 4 5 6 7 Car 3 has a changing velocity throughout, finishing at 7 m / sec Acceleration is 1 m / sec2
- 34. Quick Review • Velocity:speed of motion in a direction • Acceleration: change in velocity What causes an object’s velocity to change?
- 35. • If you’reriding 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?
- 36. Nothing will changespeed 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.
- 37. Only a forcecan change the velocity of an object. • That force can act to accelerate it NSF North Mississippi GK-8
- 38. Only a forcecan change the velocity of an object. • That force can act to decelerate it
- 39. Then why dothings 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.
- 40. Then why dothings 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.