# Kinetic Energy

## Objects in motion possesses energy which depends on their speed and mass.

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Practice Kinetic Energy

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The Bowling Ball Pendulum

### The Bowling Ball Pendulum

By pulling a bowling ball back and releasing it from rest, you can demonstrate one of the most fundamental concepts in physics: the conservation of energy. As the ball swings back, it will swing dangerously close to the person's face but never actually make contact. The conservation of energy is a topic that permeates every aspect of the physical world, and the bowling ball pendulum shows how dangerous the slightest miscalculation could be.

• Watch Paul Hewitt demonstrate the principle of the conservation of energy at the link below:
• Watch what happens when you push the bowling ball during the initial release:

#### Why It Matters

• The conservation of energy in physics states that the total change in energy in an isolated system is equal to zero. This leads to the conclusion that the total energy of the universe is constant. Energy can be converted from one form to another, such as mechanical to thermal or kinetic to potential, but the total energy is always constant. Mathematically this is represented as:

\begin{align*}E_{system}=E_{thermal}+E_{mechanical}+E_{chemical}+E_{other}\end{align*}

Credit: Ken Ratcliff
Source: http://www.flickr.com/photos/95212304@N00/2685792925

Roller coaster designers calculate specific heights needed to clear loops and inclines [Figure2]

The conservation of energy is used in almost every facet of everyday life:

• Mechanical energy is converted to thermal energy in the process of using the breaks on an automobile
• Falling water (having potential energy) is used to turn a turbine that creates electricity
• Releasing a roller coaster cart from a certain height so the cart will have enough velocity to make it through an upside down loop

#### Show What You've Learned

Using the information provided above, answer the following questions.

1. Assume you hold a ball from your outstretched arm. When you drop the ball, how much kinetic energy does it have before it strikes the ground if it had 5 J of potential energy before being dropped?
2. For the bowling ball scenario described above, where does the ball have the maximum kinetic energy?
3. For the bowling ball scenario described above, where are the two points that the bowling ball will have the maximum potential energy?

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