Investigating the relationship between the speed of a model car and its stopping distance.

Authors Avatar

Matthew Richards        5L        Mr Moncaster

Investigating the relationship between the speed of a model car and its stopping distance

Introduction

I am going to investigate the stopping distance of a model car against its speed. To investigate this relationship I will be rolling a model car down a ramp, set at different heights, measuring the speed and stopping distance for each run then averaging these results.

Predictions

The faster the model car is travelling the greater the stopping distance of the car will be.

The main reason for this is friction, there are other factors, such as air resistance, but it is very difficult for us to measure this on such a small scale so we will dismiss the possibility of the car being slowed down by this factor. Friction is the force that opposes the motion between two surfaces in contact with another.

You may be wondering how I have come about this prediction, well using scientific knowledge and my general knowledge this is the conclusion I have come to. I think it is best if I use an example to explain; taking a real car as this example, the Highway Code gives us the typical stopping distances of a car travelling at significant speeds (i.e. 20mph, 30mph, 40mph etc):

20mph        12m

30mph                 23m

40mph                         36m

50mph                                53m

60mph                                         73m

70mph                                                 96m

(This is not to scale)

This diagram includes the thinking distance of the driver car but as a human is not driving my model car this can be removed and we are left with this raw data:

(I have put speed2 on in an extra column for another prediction that I will make and explain later on in the coursework.)

This is the graph of my Highway Code data, with the distance on the y axis and the speed on the other:

As you can see there is a strong relationship between the stopping distances (not including thinking distance) and the speed and this is the basis for my next prediction:

If you double the speed then you quadruple the stopping distance.

That means that if I am travelling at 20mph and my stopping distance is

6m then if I then doubled my speed to 40mph my stopping distance would b four times that of my 20mph stopping distance, my stopping distance would therefore be 24m which I can see from my table above. If I was to draw a graph of the stopping distance against the velocity squared it would look something like this:

As I said before there is a strong relationship in these results and I would like to try and prove or disprove my prediction with my own experiment and results.

The stopping distance of the car will increase as the speed does because of the friction acting on and in the vehicle, there are several areas where friction occurs: between the car and working surface is the most obvious, but there will also be friction between the axis and chassis of the car. This friction will slow the car down, as the Kinetic energy* in the vehicle converts to heat and sound energy that dissipates into the car and surrounding atmosphere.

*Kinetic Energy – any moving body has KE and the faster it moves the more KE it has. For example as a hammer strikes a nail or a JCB levels ground it exerts a force and does work because of the KE it possesses as a result of its motion; KE is a form of mechanical energy.

The experiment that proves or disproves my predictions

Equipment:

  • 10 Wooden Blocks – for raising the height of the slope thus increasing the speed of the car. Each block is 1 cm thick.
  • Ramp – for running the car down, this is 20 cm long.
  • Light Gate / Electronic Timer– for measuring the speed of the car
  • Model Car – to run down the slope.
  • Blob of Plasticine – to attach the card to the top of the car.
  • Opaque Card – to break the light bar in the light gate thus measuring the speed.
  • 1 m Ruler – to measure the distance the model car travels
  • 30 cm Ruler – to measure the height of the blocks, therefore the height the car is being set-off from.
  • Wires – to connect the light gate and Digometre.
  • Stand – to hold the light gate in place.
Join now!

How am I going to conduct the experiment?

Set-up:

Below you can see my car with the card stuck on top of it using the plasticine, the card is exactly 5cm wide which is vital when we work out the speed the car is travelling.

This is a diagram of my experiment:

Measurements

Measuring the speed:

To measure the speed we have to use a simple equation triangle:

                

S = Speed                D = Distance                T = Time

As you can see, speed equals ...

This is a preview of the whole essay