Making a stopwatch with water!!!
An experiment to make a working stopwatch using water.
Equipment required:
An empty 2 litre plastic pop bottle and enough water to fill it up
A large washing-up bowl
A black spirit-based marker pen
Scissors
Clear sticky tape
Clock or watch with a seconds hand
Funnel
Background:
If we allow water to escape from a hole in the bottom of a container the level of the water in the container will fall. It takes time for this to happen and the longer the water is left to flow out of the hole then the lower the water level in the container becomes. This is due to the force of Gravity. We can use this in order to measure time, so we can make a stopwatch using water!
Let’s set up the equipment:
1.Spread the equipment out in front of you so you can see it all.
2. Make sure the empty plastic pop bottle is rinsed clean.
3. With one point of the scissors, make a small hole in the side of the bottle, about 3cm up from the bottom. Take care with the scissors when doing this.
4. Cut a small piece of sticky tape from the role and place it over the hole to seal it up for now.
5. Fill the bottle nearly full with water and place it in the bowl. Leave the top off.
6. Stand the bottle upright on a table and, using the marker pen, draw a line to show the position of the water level. This is the starting point and represents “0” seconds on the stopwatch, so write a “0” on the bottle next to the line.
Let’s calibrate the equipment to measure time:
7. To do this you will need the watch or clock. The idea is to mark lines on the side of the bottle after some time has passes so you end up with a scale, similar to that on a ruler.
8. Wait for the seconds hand on the watch or clock to get to the twelve and quickly remove the tape from the hole in the bottle to let the water start to flow out. Make sure all the water is caught in the bowl.
9. After 10 seconds, mark a line to show where the water level has fallen to on the bottle and write the number 10 next to the line.
10. Repeat step 9 every 10 seconds until the water stops coming out of the hole. Draw each new line below the last one at the appropriate water level.
11. Using the marker pen, write the number of seconds that each line represents next to the appropriate line, e.g. 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 etc.
12. If you have done this accurately then your bottle is now calibrated and is ready to measure time, so it can be now be used as a stopwatch.
13. Put some more tape over the hole to seal it up again.
Let’s use our new stopwatch!
14. To reset the stopwatch back to zero, place the funnel in the neck of the bottle and carefully poor the water from the bowl back into the bottle. Do not spill any.
15. The water level should now be back at the “0” mark. If you did spill any water you may have to top up the bottle to the “0” mark.
16. Let’s see how long you can go without blinking. Prepare yourself, open your eyes, and remove the tape from the hole to let the water flow from the bottle into the bowl.
17. If you blink quickly put your finger over the hole to stop the water and look at the scale to measure how many seconds you were able to keep your eyes open without blinking.
Some interesting questions!
1. Can you think of a better way of starting and stopping the water, perhaps using the screw-on bottle cap?
2. Once you have calibrated your bottle, how could you test to prove it is accurate?
3. What might affect the accuracy of your stopwatch if you use it again on a different day?
4. Are the lines you have marked on the bottle all the same distance apart? If not, why do you think this has happened?
5. What would happen if you made the hole in the bottle larger?
6. What would happen if you made a second hole in the bottle?
7. What other things can you think of to time with your new water stopwatch?
REMEMBER TO CLOSE THIS WINDOW IF YOU HAVE FINISHED LOOKING!
© South Staffordshire Water 2006