Energy 1 - An Introduction

Trust The Physics

Introduction to Energy

• Energy Cannot be Created or Destroyed
• The Total Energy in the System

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Energy

• Potential Energy
• Kenetic Energy

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Question

• Energy Conversion

Energy Cannot Be Created or Destroyed

The Law of the Conservation of Energy states that “Energy Cannot Be Created or Destroyed” , the total amount of energy in the system is always constant.

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If we started out with 100 J of energy, we will have always have 100 J of energy in the system.

James Prescott Joule

Energy Can Be Transformed!

Although the total energy in the system must stay the same, the energy is allowed to transform from one type to another. In this unit we will mainly focus on the Kinetic Energy and Potential Energy

Sample Question

At one point Samar has 100 Joules of Kinetic Energy and 20 Joule of Potential Energy while he is cruising down the Sea to Sky Highway.

• What is the total amount of energy in the system?
• If shortly after Samar has 50 Joules of potential energy, what will the kinetic energy be?
• At another point Samar has 120 Joules of potential energy, what is the kinetic energy?

Potential Energy

The potential energy, given by PE = mgh, is the energy an object has in relative to the origin point.

For example, a 1 Kg pen sitting on a 1 meter tall table will have a PE of (1 kg * 9.8 m/s² * 1 m) = 9.8 J, but in relative to the table top, the PE is “0”

PE = mgh

m = mass in kgs, g = 9.8 m/s^2, h = height in relative to the origin

Kenetic Energy

The kinetic energy is the energy an object has while travelling, it is given by KE = 0.5 mv². If an object is motionless, then it has “0” kinetic energy.

ex: Calculate the kenetic energy of a 2 kg ball travelling at 1 m/s. KE = 0.5 mv², 0.5 * 2kg * (1 m/s)² = 1 Joule

KE = 0.5 mv²

m = mass of the object, v = the velocity of the object

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Practice Question:

If a blue jay (0.5 Kg) is flying at 5 m/s at 10 m above the ground. What is its total energy? (Let the ground be the zero point for potential).

What is the kinetic energy?

What is the potential energy?

Physics Roller Coaster

The roller coaster is an excellent way to demonstrate energy conversion, when we drop from the top the the bottom, the potential energy is converted to kinetic energy, that's why we have maximum speed at the bottom

The Sk8er Boi

The demo you are about to witness shows us how energy is being transferred between potential and kinetic. Notice the points for maximum potential energy and maximum kinetic energy.