Science Experiments

What the England football team cost a nation

Sat, 5th Aug 2006

Part of the show Q&A and What Does Derek Look Like?

What you Need

1 metre of wooden stick
Drill
England flag designed to be attached to cars
Spring balance
Dave's car
Screwdriver
Cable ties or string
Two (or preferably three) people

What to do

1 - Take the stick and drill holes in it at intervals of 20cm.

2 - Attach the flag to one end of the stick with cable ties or string. You should now have what looks like a flag on a very long flag pole.

3 - Put the screwdriver through the hole 20cm from the end of the pole that has the flag attached. When the flag is out of the window, the screwdriver will act as a pivot. The amount by which the length of pole on the inside of the car is pulled will depend on the amount of force exerted on the flag outside the window.

4 - To measure the force exerted on the flag, attach the spring balance at the 40, 60 or 80cm hole. If the reading on the spring balance exceeds the top of the scale, then you should move the balance further down the pole and away from the pivot. If the spring balance is positioned at twice the distance from the pivot as the flag, then the reading from the spring balance must be multiplied by two. If it is three times the distance from the pivot (ie: at the 80cm hole) then you must multiply the reading by three.

5 - Get into your car. One person should drive while the other (one or two) people should sit in the back with the pole.

6 - Stick the flag out of the window and hold the screwdriver steady. The other person should be ready to read the spring balance.

7 - Take a reading at 40 miles per hour and 70 miles per hour. You will probably find that you need the spring balance at the 80cm hole at 70 miles per hour.

8 - Repeat the readings if you want to be thorough!

What may happen

Why does it happen?

Once we had collected our data, Dave got hold of the back of an envelope and did some maths!

power = force x speed
At 40 mph you're doing 18 m/s, and we measured a force on the flag of 3.5 N.
Putting these figures into the equation gives us roughly 63 W. This is about the same as running a light bulb.

The car is only about 30% efficient, so to work out how much power you're using in terms of petrol consumed, we must multiply this number by 3. 63 x 3 = 189W = 0.7 MJ/h
This is the amount of extra energy used each hour that you drive around with a flag at 40 mph.

Petrol contains about 30MJ/l and petrol costs about 1/l. This means that the flag costs 2p/h at 40 mph. Doing the same sums at 70 mph (31 m/s) and with a force of 6.75 N, the flag costs 8p/h at 70 mph.

But most people had two flags rather than just one, so at 70 mph this costs each car 16p/h. This doesn't seem very much, but what are the costs in terms of a whole nation?

In the UK people drive around 6000 miles per year, so 500 miles across the month of the World Cup. This works out to roughly 10 hours of driving at 70 mph, so about 1.60 per car. Say there are 20 million cars in the UK and that 10% of them sported flags. That's 2 million cars at 1.60 per car. This brings the cost of attaching England flags to cars for the duration of the World Cup to 3.2 million. HUGE!

So it seems that the England team cost the nation more than just victory. So save your petrol and throw those flags in the recycling bin!

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