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## Projectile Motion

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**Projectile Motion**3.4-3.6**Objectives**• Describe a projectile • Describe changes of horizontal and vertical components of velocity • Explain why a projectile moves equal distances horizontally in equal time intervals**Gravity**• How does gravity affect you? • Gravity is all “downwardness.” • There is no “sidewayness” to it. • Shoot and drop dart at same time. Which will hit the ground first? • Gravity does NOT take a holiday on moving objects.**Projectiles**• What is a projectile? • Projectile: • Object that moves through space acted upon by gravity**Projectile Motion**• Interactive Figure 10-4 & 10-5 (cd-rom) • There are two components of motion happening in this picture. What are they? • Vertical and Horizontal • Do they affect one another? • No! • Horizontal component of motion is independent of vertical component • What else do you notice? • Horizontal component remains constant • Both balls fall the same vertical distance in the same time (just like darts)**The rate of falling is NOT influenced by the horizontal**motion • Horizontal component remains the same! • Let's check it out Paul Hewitt Demo!! (cd-rom:10-4, 10-5)**Horizontal vs. Vertical**What do you notice?? What is the acceleration of the ball falling vertically?**The ball is in free fall vertically and moves at a constant**speed horizontally (check out the grid lines: horizontal vs. vertical) What do you notice? • Projectile Motion: • Simultaneous horizontal and vertical motions under the influence of gravity.**Projectile Motion**Notice the shape of path! • What is the name of this shape? • Parabola: • The path traced by a projectile accelerating vertically and maintaining a constant horizontal velocity.**Check Question**• If I had a slingshot and wanted to hit the door handle in the back of the room, should I aim above it, below it, or directly at it? • Directly at it. • Now, suppose that it takes the rock 1 second to reach a target. Will it fall beneath it? • Yes! How far (if the floor wasn’t in the way)? Hint: d = 1/2gt2 • 5 m • How far above should I aim to hit the target?**Upwardly Launched Projectiles**• Notice the vertical distances fallen. • d = 1/2gt2 • This is the same physics as free fall only it’s “stretched” out horizontally**Check Question**• If the cannon were aimed downward instead of upward in the last figure, how would the distances below the new “dashed line” compare?**The projectile displacements below the dashed line would be**no different. 5m at the end of the 1st second, 20 m at the end of the 2nd second, and so on. Feed the falling monkey!**Check Question**• Suppose you were flying in a plane that was traveling at 100 m/s and jumped out. Trace the path you would create after 3 seconds?**Check Question**• You are so frustrated with physics that decide to throw your text book off of the Golden Gate bridge. The speed with which the book leaves your hands is 30 m/s. • Draw the parabolic path that this projectile makes (remember, no air resistance). • How far will it have traveled horizontally AND vertically in 5 seconds? • Hint: d = 1/2gt2**Checkpoint**5m • The boy on the tower throws the ball a distance of 20m. At what speed is the ball thrown? • Equation for speed? • v = d/t • What are we missing? • Time! How do we get time ? How long does it take an object to fall 5m? You know this… • 1 sec • This means the ball travels a distance of 20m in 1 second --> velocity of ball is 20m/s 20m**Vectors**• Vectors can be used to represent the horizontal and vertical components of velocity. • What do you notice about the horizontal and vertical components? (check out Hewit’s cd-rom, 10-9) • Let's check it out!**Launching at Different Angles**• All projectiles have same initial speed, but different launch angles • What do you notice (look at the numbers . . .)? • The same range is obtained for two angles that add up to 90 degrees! • Animation • To direct water to flowers that are the farthest away, at what angle should a water hose be held? • Maximum range is attained by a 45 degree angle!**Satellites**• If superman were to throw a ball so fast that it clear the horizon, the ball would then orbit the earth and become an earth satellite. True or False?**Satellites**• Ball thrown falls 5 m after 1 second (d = 1/2gt2) • If thrown twice as fast, goes twice as far in same time. • 3 times as fast, etc. • The ball’s path curves, so does surface of earth • If ball thrown fast enough to match the curve of earth, it would orbit earth…and become a satellite.**Satellite:**• a projectile falling fast enough to fall around the earth rather than into it! • 8 km/s or 18,000 mph • Paul Hewitt explains…