Work and Momentum Notes

3.2 Energy and the Conservation of Energy

Energy is one of the fundamental quantities in our universe. Without energy, nothing could ever change. Pure energy cannot be smelled, tasted, touched, seen, or heard, but it appears in various forms, such as motion and heat. Energy travels in different ways, including light and sound waves and electricity. The workings of the universe, including technology, can be viewed from the perspective of energy flowing and transforming between different forms.

What is Energy?

Energy is defined as a quantity that measures the ability to cause change. Anything that has energy can change itself or cause change in other objects or systems. It can affect changes in temperature, speed, position, momentum, pressure, or other physical variables, and can also change materials (e.g., burning wood changes it to ash and smoke).

Examples of Energy

• A gust of wind has energy because it can move objects in its path.

• A piece of wood in a fireplace has energy because it can produce heat and light.

• You have energy because you can change the motion of your own body.

• Batteries have energy because they can power a radio.

• Gasoline has energy because it can be burned in an engine to move a car.

• A ball at the top of a hill has potential energy because it can roll down and impact other objects.

Units of Energy

The unit of measurement for energy is the joule (J). One joule is defined as the energy needed to push with a force of one newton over a distance of one meter.

• 1 joule = 1 newton × 1 meter
  If you push on an object with a force of one newton across a distance of one meter, you convert one joule of energy into motion.

Vocabulary

• Energy

• Joule

• Work

• Potential Energy

• Kinetic Energy

• Law of Conservation of Energy

Objectives

• Describe work and energy.

• Calculate potential energy.

• Calculate kinetic energy.

• Apply the law of conservation of energy to explain the motion of an object acted on by gravity.

One Calorie, often used for food, equals 4,187 joules.

What is Work?

The term "work" has various meanings in everyday language, but in physics, it has a specific definition: Work is the transfer of energy resulting from applying a force over a distance. To calculate work, you multiply the force by the distance an object moves in the direction of that force.

• If you lift a one-newton block for a distance of one meter, you do one joule of work, transferring one joule of energy from your body to the block, thus changing its energy.

• Work is done on objects; for instance, if you lift a block one meter with a force of one newton, you complete one joule of work on the block.

Energy

An object capable of doing work possesses energy. Without energy, performing work is impossible. Energy can be viewed as stored work. A falling block has kinetic energy that can perform work, such as hitting a ball and changing its motion.