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In Motion: Part 2

In Motion: Part 2. Mr. Kecman. Clas s 1. Agenda Learn about the history of force Handout for Balloon Car Race Video. Part 2: Force. History of Motion Inertia in car collisions Forces Newton's laws Momentum and Impulse Friction Braking Distance. Remember. Motion:

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In Motion: Part 2

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  1. In Motion:Part 2 Mr. Kecman

  2. Class 1 • Agenda • Learn about the history of force • Handout for Balloon Car Race • Video

  3. Part 2: Force • History of Motion • Inertia in car collisions • Forces • Newton's laws • Momentum and Impulse • Friction • Braking Distance

  4. Remember • Motion: • Defined as the process of the movement of an object from one place to another. • The study of the motion of objects and the forces that affect their motion is called Mechanics • Mechanics is divided up into: • Kinematics • Dynamics

  5. Dynamics • Is the branch of mechanics dealing with motion of objects under the action of force. • Dynamics answers these questions: • Why is the object speeding up or slowing down? • How does it turn?

  6. The Historical Development of our Ideas of Motion

  7. We will look at 3 scientists from history • Aristotle • Galileo • Newton

  8. Aristotle thought that heavier objects fell to the ground faster than lighter objects…. …and that all motion on the Earth was straight and linear. The way Aristotle thought The way projectiles projectiles moved. “really” move.

  9. Straight and linear motion: The way Aristotle “saw” As we know, or will know soon, objects fall on the Earth. objects actually fall like this in a friction-free environment vacuum.

  10. Because Aristotle was a very powerful man, his incorrect ideas were propagated for over 2000 years.

  11. Galileo Galilei (1564-1642) performed many “thought experiments” with respect to motion. From these experiments, he proposed that the motion of a falling object does not depend on mass, but on friction.

  12. Interestingly enough, it is the force of friction that stops an object. Forces aren’t actually required to keep an object in motion.

  13. This is what Galileo would have seen at Pisa—two balls with unequal masses falling in the same time. (There would have been little wind on the day of Galileo's experiment, so friction would have been minimal) http://www.youtube.com/watch?v=5C5_dOEyAfk

  14. Misconceptions about falling objects https://www.youtube.com/watch?v=_mCC-68LyZM&spfreload=10

  15. Brainiacs—Do heavy objects fall faster than light objects? Aristotle vs. Galileo http://www.youtube.com/watch?v=AYz_K3mwq6A

  16. In the absence of friction, a ball rolling down a ramp would theoretically continue moving until it reached its original height.

  17. NOTE: It is the force of friction that stops an object. Forces aren’t actually required to keep an object in motion.

  18. Newton’s 3 Laws of Motion

  19. First Law An object at rest will stay at rest, and an object in motion will stay in motion unless a force is applied to the object.

  20. Tablecloth trick http://www.youtube.com/watch?v=zWeKRMh3kT8 How to perform the coin and card stunt http://www.youtube.com/watch?v=np53X9MTKJo

  21. Amazing Bottle Tricks - Cool Science Experiment http://www.youtube.com/watch?v=cBK4wXT3FoI&feature=youtu.be

  22. Inertia The tendency of an object to resist changes in motion. Inertia http://www.youtube.com/watch?v=7LGi-Dlb8Vs

  23. Balanced vs. Unbalanced Forces

  24. Applications of the First Law • Blood rushes from your head to your feet while quickly stopping when riding on a descending elevator. • The head of a hammer can be tightened onto the wooden handle by banging the bottom of the handle against a hard surface.

  25. To dislodge ketchup from the bottom of a ketchup bottle, it is often turned upside down and thrust downward at high speeds and then abruptly halted. • The ladder on the roof of a truck which stops abruptly breaks its harness straps and slides off the top of the vehicle, becoming a dangerous projectile.

  26. Headrests are placed in cars to prevent whiplash injuries during rear-end collisions. • While riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb or rock or other object which abruptly halts the motion of the skateboard.

  27. Second Law (aka: F = ma) When a force is applied to an object, the object will accelerate in the direction of the force.

  28. Third Law For every action, there is an equal and opposite, reaction.

  29. Giant Newton’s cradle http://www.youtube.com/watch?v=mFNe_pFZrsA Newton’s cradle applet http://www.walter-fendt.de/ph14e/ncradle.htm

  30. Stomp Rocket http://www.youtube.com/watch?v=Pu_XeghO6WU&feature=related http://www.youtube.com/watch?v=i5XAuAz_4bs&feature=related

  31. Three laws of motion: http://www.youtube.com/watch?v=JGO_zDWmkvk http://www.youtube.com/watch?v=PkAO8F-Tm-w

  32. Class 2 • Video • Balloon Car explanation

  33. Force! • https://www.youtube.com/watch?v=06zCLTSaPmc&spfreload=10 • (Bill nye force) • Watch the video and answer the worksheet as best you can.

  34. Answers • 1. What puts things in motion? Forces • 2. Forces are like ___________ or ____________. (both letters start with the letter P) pushes, pulls • 3. When something is sitting still, it stays sitting still unless acted on by an ________________ ____________. When something is moving it keeps moving unless acted on by an __________________ ______________. Outside force (x2)

  35. Answers • 4. “Harder to move” is a property of matter called _________________ inertia • 5. Why does the quarter fall into the glass? (one word) inertia • 6. Things at rest stay at ___________, things in motion stay in ____________, unless acted on by an outside ______________. Rest, motion, force • 7. F= ___________ x ___________________ mass, acceleration

  36. Answers • 8. For every action, there is an equal and _____________ ________________ opposite reaction • 9. In zero gravity, do the Laws of Motion still apply? Yes • 10. Is the fire extinguisher in the room moving? Yes, everything is really moving since the earth is moving, but relative to the earth, no.

  37. Hand Out • Please stretch your legs and come pick up a Balloon Car Information Sheet

  38. Class 3 • Agenda: • Complete the booklet and stations. • If you finish early, try the Force Worksheet. Do at home!

  39. Class 4 • Agenda: • Refresh • Momentum and Impulse • WS

  40. Refresh • Aristotle • Linear motion and heavy objects faster • Galileo • Proved Aristotle was wrong • Newton • Developed 3 laws which are:

  41. Refresh • 1) object at rest will stay at rest, and an object in motion will stay in motion unless a force is applied to the object • 2) f = m x a • 3) For every action, there is an equal and opposite, reaction

  42. Momentum and Impulse Remember that math is the language of the Universe! Newton actually formulated his Second Law in terms of the change in velocity. So, if F = ma, F = m Δv Δt If we cross-multiply, we end up with FΔt = mΔv

  43. FΔt = mΔv On the left-hand side we are left with FΔt. The force applied over a certain period of time is called impulse. To increase impulse, we must increase the force applied, or the time over which we apply the force.

  44. FΔt = mΔv On the right-hand side we are left with mΔv. The product of mass and the change in velocity is called momentum, and is known as a quantity of motion. For example, a 100,000 kg train moving at 5.0 m/s has more momentum than a 10g Hot Wheels™ car moving at 5.0 m/s. It is therefore more difficult to stop a moving train than a moving Hot Wheels™ car.

  45. In order to change the momentum of an object, we must change its velocity (as we don’t want to change its mass) by applying an impulse. For example, to move a ball, we must apply a force on the ball over a certain period of time. http://www.youtube.com/watch?v=EaGUUcBTanw

  46. If the ball must move a greater distance, we may obtain greater momentum (velocity) either by increasing the force (by kicking, hitting, or throwing the ball harder) or by applying the force for a greater length of time (“following through”). http://www.youtube.com/watch?v=lBMA2wWuqh8 http://www.youtube.com/watch?v=OrLcZNG0N0I

  47. On the other hand, to bring a moving object to rest, an impulse is required to reduce the momentum to zero. In a car collision, the impulse which is most threatening to drivers and passengers is called the “second collision.” This occurs when the individual hits the steering wheel, windshield, or any other rigid object.

  48. Since impulse is the product of FΔt, when a person collides with a fixed object, the duration of time is very small and the force is very large. The result is damage to the car and severe personal injury. • How do we prevent this?

  49. To protect passengers in moving vehicles, engineers try to “cushion” the blow (reduce the force of the impact) by increasing the duration of time over which the force from the collision is applied before the momentum is reduced to zero.

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