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Free Fall

Free Fall. Up and Down. Two balls are thrown at the same initial speed, one upward and one downward with negligible air resistance. When the balls strike the ground the ball thrown upward has a speed equal to A) four times the speed of the ball thrown downward.

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Free Fall

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  1. Free Fall

  2. Up and Down • Two balls are thrown at the same initial speed, one upward and one downward with negligible air resistance. When the balls strike the ground the ball thrown upward has a speed equal to • A) four times the speed of the ball thrown downward. • B) two times the speed of the ball thrown downward. • C) the same speed of the ball thrown downward. • D) one half the speed of the ball thrown downward. • E) one quarter the speed of the ball thrown downward.

  3. Falling on the Earth • Objects fall to the earth. • Items that start by going up, stop and then fall again, reversing direction. • Items that fall from greater heights end up with more speed. • The velocity changes, there must be an acceleration.

  4. Surface Gravity • At the surface of the Earth, gravity creates a nearly constant acceleration. • This gravitational acceleration is called g. • g = 9.8 m/s2 and is directed downward. • Note that g is an acceleration. • Don’t be fooled by phrases like g-force. • g can be used as a unit of acceleration.

  5. The constant acceleration equations apply for a = -g. The position is now y, in the vertical direction. v y t t Up and Down Initial upwards velocity v0 Negative slope = -g y0 Velocity here is –v0

  6. Initial Velocity • A person throws a ball up in the air releasing the ball at 1.5 m. If it lands on the ground after 2.0 s, find the initial velocity. • Simplify the time equation, with • y0 = 1.5 m • y = 0 m • t = 2.0 s. v0 = 9.1 m/s

  7. Exceptions to Free Fall • On Earth’s surface downward acceleration is constant. • Why do we observe that different objects accelerate differently? • Friction reduces the total acceleration. • We think about velocity instead of acceleration. next

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