Investigate how the static force exerted on the front axle varies with the vertical load applied to the rear end

Diagram of apparatus:

The rear axle consists of a metal bar, placed through the drilled hole R, which is suspended from an elastic band on either side of the wooden block. The elastic bands hang of another metal bar which is held horizontally by a clamp stand. The front axle consists of a metal bar, placed through the drilled hole F, which is balanced on small wooden blocks placed on either side of the wooden block. Thus, the front axle rests all its weight on two wooden blocks placed on a mass balance. The fixed load is supplied by placing two 100g masses on the wooden block at 0.25m from the rear of the wooden block. above. The variable weight is supplied by hanging different numbers of 100g masses from the hook at the rear of the wooden block. A spirit level is placed on the wooden block in order to ensure it is level. The wooden block can be made level my adjusting the clamp stand or by raising the mass balance off the work surface using an adjustable platform.

Range of precision of instruments:

Mass Balance – Measures to the nearest gram.

• Measurement may be out by 1g
• Mass balance has a 2000g capacity

Procedure:

1. Set up the apparatus as shown above and ensure the wooden block is level, using the spirit level, with no variable weight attached.
2. Take a measurement from the mass balance.
3. Add a 100g mass to hook on the wooden block and take a measurement from the mass balance.
4. Increase the variable load by adding 100g masses and then take measurements from the mass balance.
5. Record measurements in table:

6. Use the equation F = mg where F is the force in Newton, m is the mass in kilograms and g is the gravitational field strength (9.81 Nkg-1 on earth) to work out the force applied on the rear axle (both fixed load and variable load added together) and the static force exerted on the front axle of the recovery truck.

Accuracy and Reliability

The accuracy of the results will depend on the limitations of the instruments being used, so for this investigation it would depend on the accuracy of the mass balance. Accuracy for this investigation would also depend on human error when taking readings from the mass balance, or when using the spirit level to ensure the wood block is horizontal. Accuracy is therefore a measure of the difference between an observed measurement and the true measurement.

The reliability of the results can be determined by repeating the experiment and judging the extent of the internal consistency in the individual measurements. It is a measure of the confidence which can be placed in the observed measurements as well as a measure of the reproducibility of the measurements.

Safety Precautions:

There is a danger due to the heavy loads being used. To ensure that the investigation is safe, boots with steel toe-caps must be worn or feet must be kept well away from the heavy loads.

There is also the danger of the elastic bands that hold the wooden block snapping. To prevent eye injury due to pieces of elastic shooting into eyes, wear safety goggles.

References:

Equilibrium and Statics:

Gravitational Field Strength