BuiltWithNOF
Vehicles

Vehicles and ramps are so much fun and there is lots of valuable Science and DT involved.

Ramp graph Simonside Jarrow
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Pupils of all ages can learn a great deal from rolling vehicles down a ramp. Even junk model vehicles can be tested on a ramp. Gravity, air resistance and friction can be investigated. It’s a great one for the ‘fair test’ concept and a brilliant way to introduce graphs even in year 1.

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.

Repeating 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).

Ramp graph Simonside Jarrow

This flipchart graph was produced as part of the summing up at the end of the Year 6 ‘vehicles day’ at Simonside Primary school in Jarrow. The pupils drew the main graph from a set of results obtained by one of the groups (the individual graph points can be seen). The graph is very rough but is a close approximation to an actual ramp graph drawn out on graph paper.

Graphs can sometimes be made more complicated than they actually are! It’s best to think of them as ‘measurements’ in the form of a picture. The steeper the graph line, the faster the vehicle. It’s always fun to introduce vehicle shape into the discussion. As you can see, Mr. Swift’s car is an ‘old banger’ (Postman Pat’s van) which is not very streamlined. Mrs. Hayton’s car is very sporty so has a shape which gives very little air resistance. If both cars had the same engine power then Mrs. Hayton’s car would be the fastest!

 

Friction

It may also be difficult to obtain results for very low ramp heights in the region of 10cm and below. In some cases the vehicle may only just be able to overcome ‘friction’ or could find it difficult to move at all. This is an interesting scientific point though and should be discussed. All moving systems have to overcome friction. Friction is a force which tends to prevent or oppose the motion of one surface against another. It can be both a good thing and a bad thing in real life. Cars could not travel along the road if it wasn’t for the strong frictional force between the rubber tyres and the tarmac surface – they would just slip over one another if it wasn’t for friction. But, too much friction in the moving parts of the engine, wheels and axles would mean it would be very difficult for the engine to push the car along – this is why oil is used on all of the smooth moving parts to reduce the friction and allow them to slide over one another easily.

A large space is needed for this exercise. The classroom pictured above was only big enough for 6 ramps with three pupils working together at each ramp. Another four ramps were set up in the corridor outside – not always ideal! If the school hall is available then this is the perfect venue in terms of space. One interesting advantage of the ‘corridor and classroom’ situation was that the classroom was carpeted but the corridor was not. This gave very different sets of results which promoted excellent discussion about friction on rough compared to smooth surfaces.

Vehicle rolling down a ramp Investigation No.2

The aim is to find out the effect of different surfaces on the distance travelled by the vehicle. This can be set as a challenge for the pupils. They will have to make a plan of how to carry out the investigation in a fair and proper way taking into account what must be varied and what must be kept constant in each trial or ‘run’. Since the ‘type of surface’ is under investigation then this is our key variable or ‘controlling variable’. The distance travelled must be measured for each type of surface so that a comparison can be made. The important difference in this investigation compared to investigation No.1 is that the slope height must be kept constant each time so pupils will have to choose one particular slope and not change it!

The vehicle should travel furthest after travelling down the slope with the least friction since friction opposes the motion of the wheels and opposes the force of gravity which is causing the vehicle to move.

A very thorough investigation can be carried out by choosing 3 different surfaces and producing a graph, as in investigation No.1, for each surface. All three graphs could then be drawn on the same piece of graph paper and the slopes of the graphs compared. This is a good way to show how important graphs can be in science investigations and how much can be deduced by comparison. The slope of a straight line graph has particular significance since it allows us to make conclusions about ‘proportionality’.

The different surfaces could be: carpet, wood (hardboard usually has a rough side and a smooth side), plastic, lino, corrugated card.

Vehicle rolling down a ramp Investigation No.3

The aim is to find out the effect of changing the mass of the vehicle on the distance travelled.

(this is a real challenge since the theory of Gravity tells us that objects of different mass should fall at the same speed under the effect of gravity – similarly, the speed of a vehicle rolling down a ramp should be independent of it’s mass! Friction plays a big part in the results of this investigation and it can provide a real challenge for the brighter ones in the class.

 

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