Kinetic energy physics exercise

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Discussion Overview

The discussion revolves around a physics exercise concerning the kinetic energy of a ball dropped through a slide, focusing on the concepts of energy conservation, potential energy, and kinetic energy. Participants explore the implications of these concepts in the context of a velocity-time graph and the behavior of the ball as it transitions from vertical to horizontal motion.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the concept of constant velocity when the ball reaches the bottom of the slide, questioning whether the presence of kinetic energy implies that a force must be acting on the ball to cause acceleration.
  • Another participant asserts that the ball's total energy remains constant throughout the experiment, emphasizing that energy is converted from potential to kinetic without the need for additional forces to gain energy.
  • A participant seeks clarification on the energy state of the ball when it is at rest on the floor, questioning if it has zero energy and whether energy is created when lifting the ball to the top of the slide.
  • A response clarifies that while energy is used to lift the ball, it is not created; rather, work is done to convert biochemical energy into potential energy, maintaining the principle of conservation of energy.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the conservation of energy and the implications of kinetic and potential energy. There is no consensus on the initial energy state of the ball or the interpretation of constant velocity in the context of forces acting on the ball.

Contextual Notes

Some assumptions about energy states and the definitions of kinetic and potential energy are not fully explored, leading to unresolved questions about the initial conditions of the ball and the nature of energy transfer during the lifting process.

Who May Find This Useful

This discussion may be useful for high school students studying physics, particularly those grappling with concepts of energy conservation, kinetic energy, and the dynamics of motion in gravitational fields.

Fabian901
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I'm going through a physics exercise at high school level. A ball is dropped through a slide and when it reaches the bottom of the slide it will travel horizontally. Assuming there is no energy loss due to friction or air resistance draw a velocity time graph.
I tried working it out, the answer on the book says that when the ball reaches the bottom of the slide it will start moving horizontally with a positive constant velocity. I'm a bit confused on the constant velocity part. When the ball is moving horizontally, it obviously has KE. And the fact that it has energy doesn't it mean that there is a force applied through a distance, and therefore it should accelerate?
Many thanks in advance!
 
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The ball's total energy is constant through the entire experiment. A force is only required to gain energy. All this experiment does is convert potential energy to kinetic energy.
 
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Many thanks Russ! I don't think I understand the principle of conservation of energy that well then. Imagine that before someone put the ball on top of the slide the ball was standing on the floor with no motion, what was the energy of the ball standing still on the floor? Is it 0 joules? Was energy being created to place the ball on top of the slide? If so, wouldn't this contradict the principle of conservation energy which states that energy cannot be created or destroyed?
 
Fabian901 said:
Imagine that before someone put the ball on top of the slide the ball was standing on the floor with no motion, what was the energy of the ball standing still on the floor? Is it 0 joules?
Measured with respect to the floor, the mechanical energy of the ball would be zero. (0 gravitational PE + 0 kinetic energy)

Fabian901 said:
Was energy being created to place the ball on top of the slide?
Energy was used to lift the ball and place it on the top of the slide, but that energy wasn't 'created'. For example, if a person lifted it, that person had to do work on the ball, essentially converting some biochemical energy to give the ball increased potential energy.

Fabian901 said:
If so, wouldn't this contradict the principle of conservation energy which states that energy cannot be created or destroyed?
Not to worry. Conservation of energy is safe and sound!
 
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Thanks a lot for the help guys!
 

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