Ramp and toy cars

We do a lot of activities that introduce various aspects of science to my sons, but I wanted to do something which would start to introduce some of the concepts of scientific methods - not just making hypotheses about what may happen and trying it to find out, but about how we can change a single variable and observe the effect, of collecting data systematically and using it to reach a conclusion.

We've talked quite a lot about speed recently, mostly of real cars driving - are they obeying speed limits, what speed limit signs mean and how speed is about how fast something goes and this means how far it can go in an amount of time.  I thought we could try a very simple investigation using a cardboard ramp and a toy car to build on this. 

Ramp and car

We used some sturdy corrugated card (you could use a piece of wood, it needs to be rigid) combined with some Duplo blocks (any building blocks that interlock and form a stable tower would work), a toy car and a timer (mobile phone, not ideal as it's got more buttons than you need, but it worked ok).  The basic premise was to measure how long the car took to reach the bottom of a ramp if it started at the top with no pushing, and try this for different angles of slope (heights of Duplo tower).  The car accelerates down the ramp from a starting point of zero velocity, but I glossed over acceleration as it was too hard a concept to start with, and we just talked about speed, distance and time.

We started off trying to measure the speed with a height of 1 Duplo block, which wasn't enough to get the car moving.  My son added a row at a time until the car would roll until it reached the bottom (for us, this was 5 blocks tall).  Then I released the car whilst he timed (the trick here was to let go as he tapped the start button, rather than trying to say start and get him to press).  Before we started we discussed how long a second was, how many are in a minute and what a decimal point means (the latter I don't think went in, although he did realise the numbers after the point were smaller than seconds).

The only action shot I got!

There were lots of nice talking points about what made things 'fair' i.e. whether the car started in the same place, whether it had a push or standing start, whether he pressed stop quickly enough, whether the car went off the side of the ramp and therefore didn't travel as far.  We talked about these as we measured, built higher, and repeated it.  We started off with my son doing the writing, but he's not a huge fan of putting pen to paper and asked me to take over!  I didn't get any good photos from this as I was too involved in letting go of the car and writing...

We got to 20 Duplo blocks, and the ramp became increasingly hard to balance without it slipping, and the time taken for the car to travel the length of the ramp approached half a second which was hard for him to time, so we gave up.  We had a look at the results we'd written down and he could see that the numbers of seconds got smaller as the height of the ramp increased, so it took less time for the car to travel down a steeper ramp i.e. it was faster.

Later he asked me how fast the car had been going on the steepest ramp, and whether it was faster than the 20mph speed limit in our street.  I explained that we needed to know the distance the car travelled as well as the time to work out the speed (average/mean speed as it accelerates).  He measured the length of the slope using Duplo blocks.  I decided not to try and explain that converting from Duplo blocks per second to miles per hour wasn't straightforward, and just produced the answer for him - the fastest speed we recorded was just over 3mph (actually not for the steepest ramp, but the timing accuracy was dubious!).

I wasn't sure how engaging this activity was, but he wanted to do it again a week or so later, with a different car so he must have enjoyed it as much as he appeared to at the time!  I suggested that we repeated the timing three times at each height so we could see if any of our measurements were much higher or lower than the others.  We did, and he noticed a few outliers and we talked about why they might have happened (mostly that he missed the stop button the first time!).  The second attempt was cut somewhat short by the smaller one insisting that he needed to play with the toy car the older one had chosen for his experiment and accidentally sitting on the ramp in the process of trying to take it - the corrugated cardboard was sturdy, but not sturdy enough!  The big one took it remarkably well...

I think we'll give some more activities with a more structured approach to experimenting a go sometime soon as he seemed to enjoy it.