Mechanical energy and work done

In a nutshell

When energy is transferred using a force this is called work done. Mechanical work can be calculated by multiplying force and distance.

Equations

Word Equation	Symbol Equation
$work \space done = force \times distance$	$W = F \times s$

Variable definitions

Quantity Name	Symbol	Unit Name	Unit
$force$	$F$	$newton$	$N$
$distance$	$s$	$metre$	$m$
$work \space done$	$W$	$joule$	$J$

Work done

Definition

Work done is the energy transferred from or to an object using a force. Work can be done either mechanically or electrically. This allows energy to transfer from one store to another.

Work done	Examples
Mechanically	Pushing a table, skydiving, running
Electrically	Light bulb turning on, signals being sent from your brain to your body

Mechanical work

Mechanical work is done when a force is applied to an object.

Example

Describe the energy transfers for a skydiver using an energy transfer diagram.

$\boxed{gravitational \space potential \space energy} \xrightarrow [mechanically]{energy \space transferred} \boxed {kinetic \space energy}$

You can calculate work done by using the following equation.

$work \space done = force \times distance \\ \ \\ W = F \times s$

Example

The force needed to push a bike for $5 \, m$ is $50 \, N$ . How much work is done?

First select the correct equation:

$W = F \times s$

Then, substitute in the values:

$W = 50 \times 5$

Don't forget to include your units in your final answer:

$250 \space J$

$\underline{250\,J}$ of mechanical work was done to push the bike.

Electrical work

Electrical work is done when an electric charge flows. For example, the device you are on now is doing electrical work in order for you to use it. A force is needed in order to do this, but you don't need the equation for this just yet.

Example

Describe the energy transfer between a battery and a light bulb using an energy transfer diagram.

$\boxed{chemical \space energy \space in \space battery} \xrightarrow[electrically] {energy \space transferred} \boxed {thermal \space energy \space and \space radiation}$ 