Wednesday, June 3, 2015

Inertia Exploration

Exploring Inertia with Students

What is Motion?
Energy is the ability to do work.  In order to do work a force must be applied.  A force can be a push or pull that causes an object to move, stop, or change direction. A force strong enough creates motion.  Motion is the act of moving.   If there is not force there will be no movement. 
Energy can be kinetic or potential.  Kinetic energy is energy of motion.  Potential energy is stored energy based on its' position or condition.  When you hang from the monkey bars you contain lots of potential energy.  The potential to fall.  When you let go you now have kinetic energy.  You fall to the ground. 
Exploring Newton’s Laws of Motion
The first law of motion is inertia.  All objects have inertia.  The law states that an object will stay at rest unless a force acts on it and an object will keep moving until a force stops it.  When 5 pennies are stacked on a piece of cardboard on top of a can they are at rest. The pennies are not moving and have no kinetic energy.  The pennies have the potential to move if the cardboard is pulled out from under the pennies.  

When the cardboard is pulled out from under the pennies the pennies do not move.  The force was applied to the cardboard.  The pennies then lose the support of the cardboard and fall into the can.  It takes some practice to pull the cardboard straight out without having it push on the pennies.  If that happens the pennies are not at rest and will go flying into the air.  Simply, if nothing touches the pennies they will not move.
If the pennies are at rest, why did they fall into the can?  Without the cardboard the force of gravity
pulled the pennies into the can.  The pennies had Gravitational potential energy.  Gravity is the attraction of matter to each other.  It is an invisible, weak force.  The larger the object the more gravity it has.  When on earth, it has the largest gravitational pull. The pennies fall straight towards the earth.  This is a great  trick and demonstration showing that an object only moves if a force is applied. 


Can you remove the card without touching the penny?

 Penny  Note card  Index Finger
1.Using your non-dominant hand balance the note card on your index finger.
2.The penny is then placed on the note card directly above your index finger.
3.Using your dominant hand flick the paper straight out.  The goal is to get the penny to stay on your finger.
Explanation and Tips
This can be done, but it is a challenge.  It is so exciting when you get it.   You will realize that you need to move the card without affecting the penny.  The tough part is going to be to keeping your index finger steady.  Do not give up.  This demonstration proves perfectly that an object will not move unless a force is applied.  The wonders of inertia.

Turn it into an experiment.  What if you try other coins?  Will a quarter work?  Can you stack more pennies on top?  The answer will surprise you because the heavier the object the more it will resist movement.  Give it a try.
Here are some more great inertia demonstrations and investigations.

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