Nearly summer! Here are some cool experiments to start you off

If you live in England, you will most likely have half a week of school left before you can get up late in the mornings, wear “your own” clothes and spend your time the way YOU like. Although, if you are ever stranded inside on a rainy day, I have a few fun experiments for you to try, passing the time…

Hit the Floor

You will need:

  • a table or a desk, standing on flat ground
  • two coins of the same value
  • a stopwatch (optional)
  • two objects of different masses
Bangle and dictionary
Bangle and dictionary - which will land first?
  1. Line the coins up on the edge of your table.
  2. At the same time, gently push one coin off the side of the table, and flick the other one away (but not up) from the edge.
  3. Which coin lands on the floor first?
  4. Line your two objects of different masses up against the edge of the table.
  5. Gently push both of them off the edge.
  6. Which lands first?

Explanation: This is gravity at its best. Imagine the gravitational force like a piece of invisible string pulling the objects towards… who-/whatever is holding the other end of the string! In this case, it is the Earth. The Earth always pulls the string with the same force, in the same direction – “down”, as explained two blog entries ago. So, regardless of whether the objects travel different distances (the coins), or have the different masses (the bangle and the dictionary), because the Earth itself is so massive, the force that all of these experience is the same. They should all hit the floor at the same time.

Edible Lenses (Adapted from television show Backyard Science)

You will need:

  • a packet of jelly mix
  • a jelly mould (preferably flat-bottomed, otherwise, slice the top/bottom off to make  two flat sides)
  • a round cookie cutter
  • a table knife
  • a comb
  • a light source, e.g. a torch
  1. Make the jelly and let it set firmly in the mould – let it become a little bit more solid that it should be.
  2. Tidy up the top and bottom with the table knife so that you have a flat piece of jelly of even thickness.
  3. Use the cookie cutter to remove a round block of jelly, then cut it in half along the diameter.
  4. Now, you have a thick, semi-circle of jelly. Shine the torch THROUGH the comb (teeth pointing downwards), so that you get many thin beams of light, onto the flat side of the semi-circle.
  5. What happens to the beams of light on the other, curved, side of the semi-circle?
  6. Cut a large square around the hole made by the cookie cutter (in the original sheet of jelly), and cut that in halves, down the middle. Shine the torch through the comb as before on the outside of the “hole”, i.e. a side of the square; now what happens to the light beams?
  7. Repeat the experiment with different shapes of jelly to see what other patterns you can make.
  8. Enjoy the jelly, bon appétit!

Explanation: When light passes through a medium (something that is not vacuum), it gets refracted. The speed of the beams usually slows down, as the light gets bent away from the path in which it entered (perpendicular, in this case).

Convex and concave lenses
Convex and concave lenses converge and diverge (respectively) light beams entering from the left.

[2]

Measuring the Speed of Light (c) (Adapted from Imperial College Physics Outreach)

This is something we often demonstrate on open days, as a way of relaying that science is not an elitist topic, but is readily accessible to all (no patronisation intended). Now, the result of this experiment is not really all that accurate, but it is plausible as a method to find the required constant. See the explanation for further details.

You will need:

  • a chocolate digestive biscuit (on a plate)
  • a microwave
  • a ruler
  • a calculator
  1. Place the chocolate digestive biscuit CHOCOLATE SIDE UP on the plate.
  2. Put the whole thing in the microwave at high power for approximately one minute – small peaks should have formed in the chocolate.
  3. Using the ruler, measure the distance between the peaks in the chocolate. Convert that into metres. (1000 millimetres = 100 centimetres = 1 metre)
  4. The average frequency of a commercial microwave oven is around 2.45 GHz [1], which is 2.45 × 109 Hz. Multiply the distance found in part 3 with this value, and the result is your very own record of the speed of light!

Explanation: The microwaves in the oven will melt the chocolate, and resonate with the material, this cause the little peaks to arise; they are the nodes of a standing wave, formed from resonance. One of the wave equations is c=fλ, where c is the speed of light (measure in metres per second), f is the frequency (in Hertz, or Hz) and λ (greek letter lambda) is the wavelength (in metres); this was used to find the speed of light, which, for a vacuum, is 299,792,458 metres per second, and often approximated to 3 × 108 metres per second.

Job well done, I would say.

[1] “Frequency of a Microwave Oven” – http://hypertextbook.com/facts/1998/HowardCheung.shtml

[2] “Lens, Light and Your Eyes” – http://www.mysciencesite.com/optics4.html

299 792 458 m / s

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2 thoughts on “Nearly summer! Here are some cool experiments to start you off

  1. Good stuff, good stuff! Some interesting ways to while away the rainy afternons. I can’t wait to try those jelly lenses!
    Keep up the good work 😉

  2. Hello again! I had a little idea that might add to your speed of light experiment. In place of the chocolate biscuit a plate of grated cheese could be used instead. Increased size might allow for multiple measurements and then you could get an average (the physicsts favourite :D)
    Happy blogging!

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