Work done (Edexcel GCSE Physics Combined Science): Revision Notes
Work done
Work done
Formula
Key Points
- Where Work Done, , is in joules , the force, , is in newtons (N), and the distance, , is in metres .
- Where distance is the distance moved along the line of action of the force.
Definition
Work done is when energy is transferred from the object doing the work to another form.
Examples:
- If a book is lifted 1m in the air and 2m to the right.
- Work is done (against gravity) when moving 1m vertically, as that is in the direction of the force (gravity).
- Energy is transferred from your muscles to the book, increasing its gravitational potential.
Joules
- One joule of work is done when a force of one newton causes a displacement of one metre.
Friction
- Work done against frictional forces causes a rise in temperature of the object.
Work Done in a Spring
Formula
Key Points
- When a force stretches or compresses a spring, the spring does work.
- Elastic potential energy is stored in the spring.
- Provided it does not inelastically deform:
- The work done on the spring equals the elastic potential energy stored.
Springs
Key Points
- To stretch, bend, or compress an object, more than one force must be applied.
- If a single force is applied, the object will move in the direction of the force rather than changing shape.
- To stretch an object, forces must be applied in opposite directions on either side.
- If an object is fixed at one end and a force is applied at the other, the fixed point provides a counteracting force, allowing the object to stretch.
Deformation
Deformation refers to a change in the shape of an object due to the application of forces.
Types of Deformation
- Elastic Deformation:
- The object returns to its original shape after the force is removed.
Example: An elastic band stretches when pulled and returns to its original shape once the pulling force is removed.
- Plastic Deformation:
- The object does not return to its original shape after the force is removed, leading to a permanent change.
Example: A spring that has been stretched too far and does not return to its original length.
Calculating Work Done
The amount of work done on an object due to a force can be calculated using the following equation:
- is work done in Joules (J)
- is force in Newtons, (N)
- is the distance in metres (m).
1J of work is done when a force of 1N moves an object through a distance of 1m. Therefore 1 Joule = 1 Newton-meter.
Example: Calculating Work Done A man pushes a box through a distance of 12m, and he exerts 14N of force on the box. Calculate the work done by the man. Ignore the frictional force.
[2 marks]
Using the work done equation:
Substitute in the values:
=14×12
Calculate the answer:
=168J or Nm