A Game Of Inertia

tableclothtrick2 Our eldest Little Spark turned eleven this week so we have been busy devising games and party tricks for our party this weekend.  Now while studying Newton’s laws of motion might not seem like everybody’s idea of a good party, especially after a week of school exams, we’ve come up with a game that seems to get our Little Sparks all fired up.  There is both tension and suspense, will the player quite literally be able to pull this one off?

You can, of course, use these ideas to help you with your science projects!

To play our game of inertia, you will need the following:

  • A group of willing players around a table (although I have been practising this by myself and having fun!)
  • A thin paper napkin or a cloth without seams, a piece of printer paper.
  • Wooden building blocks – you can experiment with all sorts of objects, but just to be on the safe side not your Mum’s best crystal wine glasses!

How to play:

  • Start by placing the napkin on the table so that most of it drapes over the edge. On top of this place two bricks one on top of the other.
  • Each player must now take it in turns to see if they can remove the napkin without causing the bricks to topple. The first time round the players might struggle to do this, the trick is to whip the napkin away as quickly as possible to minimise any friction between the cloth and the bricks.  Holding out the napkin and administering a karate chop is highly effective.
  • As players develop confidence they have to add more and more bricks to their tower with every round.
  • The player who can perform this trick with the highest tower is the winner!

karate chop

What happened here? The Science Behind The Game:

Newton’s first law of motion states that an object at rest will remain at rest (a state of inertia) unless acted upon by a force. In other words something that isn’t moving isn’t going to move unless something makes it.  This is the law of inertia. Similarly an object that is in motion will remain in motion until acted upon by a force.  If you have a stable object (hopefully your well constructed brick tower) there is no reason for it to move unless you push it or wobble the table or there is an earthquake. (Some party this is turning out to be!) These are all forces that will cause the object to move.

Friction is another force that could cause an object to move.  If you cause too much friction when you try to pull your napkin out from under the bricks your tower will topple, so of course the trick is to do it as quickly and as smoothly as possible to reduce any friction.  Gravity is another force at work here acting in your favour by ensuring the bricks remain grounded!

Take It Further:

Put your brick tower on your napkin and slowy pull the napkin towards you.  What happens?  The bricks will probably move with the napkin but remain fairly stable.  Try this again start pulling slowly and then suddenly jerk it quickly.  Observe and describe what happened.  While you pulled slowly the brick tower and napkin were in uniform motion but the sudden acceleration probably caused your tower to topple backwards.

Think about getting on a bus  where there is standing room only.  When the bus suddenly moves off you have to steady yourself to stop yourself from toppling backwards.  Once the bus is making steady progress you are able to stand without having to steady yourself, just like your bricks when you pull the napkin slowly.  However, everytime the bus makes abrupt changes in speed you will have to hold on and if it comes to a sudden stop you will probably lurch forward.

Battery In A Bottle:

Here’s another neat party trick for you that demonstrates inertia.  You need a bottle, an index card or a playing card and an AA battery.  Set your equipment up as shown below making sure the battery is positioned directly above the bottle opening.  Ask your guests (or classmates if you are doing a science project) if they can get the battery in the bottle without touching the battery.  Here’s what you do!  Using your thumb and middle finger flick the side of the card as hard as you can.  The card will shoot out from underneath the battery.  The law of inertia means the battery will stay where it is above the neck of the bottle until gravity acts upon it and it falls down into the bottle.  Have fun!

battery in a bottle


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