Vehicle rolling down a ramp Investigation No.1
The aim is to find out the effect of changing the slope of the ramp on the distance travelled.
Everyone knows that a bicycle does not need to be pedalled down a hill because it will be pulled down to the bottom by the effect of gravity. In fact you might have to keep the brakes on because gravity causes you to go faster and faster as you make your way down the hill. Gravity causes a falling or freewheeling object to ‘accelerate’.
The ramp investigation allows you to accelerate a vehicle and reach a final speed which depends upon how steep the slope of the ramp is. The faster the vehicle is travelling when it reaches the bottom of the ramp then the further it travels on a level surface after leaving the ramp.
Any vehicle can be used as long as it can freewheel and stay in a reasonably straight line. You will have to practice releasing the vehicle without pushing it and making sure that the method of release is the same for all trials. The height of the ramp is adjusted by the same amount each time and steps of about 5cm give reasonable results.
In all proper scientific investigations the results are obtained from repeating the same experiment over and over again. If a single result was relied upon then what if a mistake had been made which nobody spotted – the experiment would be invalid. For each height of the ramp the vehicle should be tried 3 times and the distances recorded. The results of the three trials can be averaged or plotted as points on the graph – by plotting them all on the graph it is possible to spot the ones which might be in error as these will show a large deviation and can be discounted. If widely differing results are obtained from the same ramp height then the method of release of the vehicle should be carefully checked because it may mean the vehicle is being released in a slightly different way each time.
A table of results should be made and a graph can be drawn as shown
The results for slope heights of 10, 15 and 20cm produce a good straight line which shows that the distance travelled by the vehicle is directly proportional to the height of the ramp. This is what is expected.
However, as the ramp height increases to 25cm and above things seem to go wrong! The distance does not increase as before with height and the graph line becomes a curve which tails off. This is because the slope of the ramp is becoming so great that the vehicle is ‘bumping’ the ground as it leaves the ramp to travel along the level surface. This causes the vehicle to lose some of it’s ‘energy’ in the ‘impact’ and so it doesn’t go as far as would be predicted from the graph prior to the 25cm mark. So, above 20cm the test is not really a fair one because there is a marked effect from the vehicle crashing into the ground because the slope height is too great.
Pupils might suggest ways of overcoming this by adding a smoothly curving strip of card near the end of the ramp to prevent the harsh bump on meeting the level surface.
You may simply wish to increase the number of trials in the 10 to 20cm region by trying ramp heights of say 8, 10, 12, 14, 16, 18, 20, 22cm. This gives more results with which to draw the graph and gives a truer picture of what is happening (in reality three results is not enough to allow serious conclusions to be made).