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# Projectile motion

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### Projectile motion

1. 1. Projectile Motion and Free Fall vs Terminal Velocity
2. 2.  If James is holding a bullet at the same height Emily is holding a gun, and James drops the bullet at the same time Emily shoots the gun, which bullet will hit the ground first?
3. 3.  They will land at the same time!  Horizontal acceleration does not affect vertical acceleration.  Both bullets will accelerate vertically at 9.8m/s2
4. 4. Projectile Motion  Projectile Motion is the curved path an object follows when thrown or propelled near the surface of the Earth.  It has two components:  Horizontal  Vertical …and they are independent of each other!
5. 5. Does horizontal Motion affect Vertical Acceleration? It doesn’t, it doesn’t, no seriously… IT DOESN’T!!!
7. 7.  I was there too, and I timed it: The bullets took two seconds to hit the ground.  What was their final speed in the vertical direction? and  What was their final speed in the horizontal direction if the initial speed in the vertical direction was 100m/s (Let’s pretend they are in a magical place with no fluid friction)
8. 8. For the horizontal… 100 meters per second, of course!
9. 9. 9.8m/s2 In the vertical…  ΔV=gt  ΔV=(9.8m/s2)(2s)  ΔV=19.6m/s 9.8m/s2
10. 10.  What if Emily was holding the gun at an upwards angle so the path of the bullet looked like INSTEAD OF Would the bullet James dropped land first, or the bullet from Emily’s gun?
11. 11.  This time James’s bullet will land first.  By tilting the gun upwards, Emily gave the bullet an initial velocity in both the vertical and horizontal direction. Gravity will have to decelerate the bullet as it goes up before it pulls the bullet down to Earth.
12. 12.  If you were able to throw a ball really far (beyond the horizon)and really fast, would it ever hit the ground?
13. 13. NO!  Gravity would pull the ball down towards the surface of the Earth, but since the Earth is curved, it is always bending away from the ball.  You could say the ball would be in orbit because it is in free fall and has horizontal velocity
14. 14. Free-Fall  Free Fall occurs when the only force acting on something is gravity.  Since outer space is a vacuum, there is no fluid friction acting on the ball- only gravity
15. 15. Space Shuttle in Orbit
16. 16. On Earth…  Fluid friction prevents an object from being in free fall on Earth.  As an object falls on Earth, the upward force of air resistance increases until it matches the downward force of gravity  When this happens, the net force is zero, acceleration stops, and the object falls at a constant velocity.  Terminal velocity is the constant velocity at which a falling object travels when the size of the upward force of air resistance matches the size of the downward force of gravity
17. 17. Terminal Velocities  Person: can be between 53m/s and 76 m/s (or 119170mph)  What factors can you think of that would change someone’s terminal velocity?
18. 18.  Terminal velocity depends on:  Surface area  Mass  Someone with a small surface area and a high mass will reach higher speeds than someone with a large surface area and small mass
19. 19. It’s raining cats and dogs!  Do cats really have 9 lives?  Or do they have a nonfatal terminal velocity of 60mph because of their ability to “parachute” themselves?
20. 20. 1987 Study from Journal of American Veterinary Medical Association  Studied 132 cats  Up to 7 stories, injuries increased with height  At 7 stories and above, injuries sharply declined  After 5 stories of falling, cats reach terminal velocity  One cat survived a fall from 46 stories