Investigating Force & Extension (Oxford AQA IGCSE Combined Science Double Award)

Investigating Force & Extension

Aim of the experiment

•  The aim of this experiment is to investigate the relationship between force and extension for a spring

Variables

• Independent variable = Force, F

• Dependent variable = Extension, e

• Control variables:

  • Spring constant, k

Equipment

Equipment list

• Resolution of measuring equipment:

  • Ruler = 1 mm

Method

Equipment for investigating the extension of a spring

1. Align the marker to a value on the ruler with no mass added to the spring, and record this initial length of the spring

2. Add the 100 g mass hanger onto the spring

3. Record the mass (in kg) and position (in cm) from the ruler now that the spring has extended

4. Add another 100 g to the mass hanger

5. Record the new mass and position from the ruler now that the spring has extended further

6. Repeat this process until all masses have been added

7. The masses are then removed and the entire process is repeated again until it has been carried out a total of three times, and an average length is calculated

Example results table

Analysis of results

• The force, F added to the spring is the weight of the mass

• The weight is calculated using the equation:

• Where:

  • W = weight in newtons (N)

  • m = mass in kilograms (kg)

  • g = gravitational field strength on Earth in newtons per kg (N/kg)

• Therefore, multiply each mass by gravitational field strength, g = 9.8 N/kg, to calculate the force, F

• The extension of the spring is calculated using the equation:

Extension = final length – original length

• The final length is the length of the spring recorded from the ruler when the masses were added

• The original length is the length of the spring when there were no masses

1. Plot a graph of the force against extension

2. Draw a line of best fit

3. If the graph has a linear region (is a straight line), then the force is proportional to the extension in this region

An example of a force-extension graph

Evaluating the experiment

• Consider any systematic errors or random errors

Systematic errors:

• Make sure the measurements on the ruler are taken at eye level to avoid parallax error

Random errors:

• The precision of the experiment is improved with the use of a pointer at the bottom of the spring

• Wait a few seconds for the mass to become stationary after it is added, before taking the readings for its length

• Check that the spring has not gone past its limit of proportionality otherwise, it has been stretched too far and will no longer obey this relationship

• Make sure the measurements are taken from the same point on the bottom of the spring every time

Safety considerations

• Wear goggles during this experiment in case the spring snaps

• Stand up while carrying out the experiment making sure no feet are directly under the masses

• Place a mat or a soft material below the masses to prevent any damage in case they fall

• Use a G clamp to secure the clamp stand to the desk so that the clamp and masses do not fall over

  • As well as this, place each mass carefully on the hanger and do not pull the spring too hard that it breaks or pulls the apparatus over