Energy

 

Energy cannot be destroyed or created, only converted from one form to another. When a car runs, chemical energy from the fuel converts into kinetic energy

Examples of energy include:

  • Light

  • Heat

  • Kinetic

  • Gravitational Potential

  • Electrical Potential

  • Chemical

  • Sound

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Work Done and Friction

In reality, energy doesn’t entirely convert from one form to another. Some energy can be lost in the process by conversion to different forms of energy. For example, when you drive a car you are converting chemical energy from the fuel into kinetic energy. Some of the kinetic energy will be lost due to frictional forces by the wind and through the tires.

Work done is the energy required to move an object a certain distance. It can be calculated using this equation:

Ew = F x d

So, if you are asked for or given distance, force or Energy, you can simply apply this equation.

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Kinetic Energy

Kinetic energy is the energy of movement. Chemical energy is converted to kinetic energy when animals move. Gravitational potential energy is converted to kinetic energy when an object is dropped from a height. Electrical potential energy is converted to kinetic energy when a motor is linked to a circuit.

Kinetic energy is dependent on the mass of an object as well as its velocity:

Kinetic energy = 1/2 x mass x velocity^2

Kinetic energy is measured in Joules (J)

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Gravitational Potential Energy

Gravitational Potential Energy is the energy that an object gains when it is pulled away from a gravitational force. So, if you lifted a chair off of the floor, it gains the “potential” to accelerate towards the Earth.

The gravitational potential of an object is dependent on mass, gravitational field strength and height:

Gravitational Potential Energy = Mass x Gravitational Field Strength x Height

The gravitational field strength of Earth is 9.8m/s^2.

The gravitational field strength of other planets in our solar system is provided in the data booklet.

The gravitational field strength of the weight in the diagram can be calculated as follows:

Ep = mgh

Ep = 15 x 9.8 x 1.5

Ep = 220.5J

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Combining Energy Equations

In National 5 Physics, we need to be able to combine equations with similar properties, and use them interchangeably. As the subject of the formula for the kinetic energy and the gravitational potential energy is Energy in Joules, we can combine these equations.

Therefore, if an equation provides you with most of these components (mass, velocity, gravitational field strength (which you already know is 9.8), height, energy), you can figure out the missing value.

A newton’s cradle converts gravitational potential energy into kinetic energy on one end, and kinetic energy into gravitational potential energy on the other end.

Key Points!

  • Energy conversion

    Energy cannot be destroyed or created, only converted from one form to another.

    Know examples of energy types.

  • Work Done and Friction

    Work done is the energy required to move an object a certain distance.

    Ew = F x d

  • Kinetic Energy

    Kinetic energy is the energy of movement.

    Ek = 1/2 m x v^2

  • Gravitational Potential Energy

    Gravitational Potential Energy is the energy that an object gains when it is pulled away from a gravitational force.

    Ep = m x g x h

  • Converting between Gravitational Potential and Kinetic Energy

    Be able to combine the kinetic energy and gravitational potential energy equations.

Any Questions?