Inertia: Investigating Forces

Investigating forces






index card
drinking glass


Lay the index card over the mouth of the glass. Place the coin on top of the card, centered over the mouth of the glass. Flick the card with your finger so that it flies off horizontally to the surface where glass is resting. You should see the card quickly move forward and the nickel drop down into the glass, unaffected by the card.


The stationary card and coin are originally at rest. They remain motionless because of their inertia. Inertia is the tendency of a material not to change its motion or state of rest. When the card is flicked, it slips under the stationary coin. Gravity pulls the coin down into the glass.


Purpose: To compare the insulating properties of paper and Styrofoam cups

Materials: 1) 2 ice cubes of equal size

2) Two 10-ounce (300-ml) paper cups

3) Two 10-ounce (300-ml) Styrofoam cups

4) Timer

Procedure: 1) Put an ice cube in one of the paper cups.

2) Slip the second paper cup inside the first one so that it rests on top of the ice cube.

3) Repeat steps 1 and 2, using the 2 Styrofoam cups.

4) Lift the tops cups and observe the ice cubes once every 5 minutes. Continue until one of the ice cubes completely melts.

Results: The ice cube in the paper cube melts first.

Why? : Styrofoam is a better insulator than paper. This is due to the amount of air trapped in the Styrofoam material. Air, like most gases is a poor conductor of heat because the particles in a gas are far apart. Gas particles don’t bump into each other very often, so gas does not transfer heat from one particle to the other very well. Since gases don’t conduct heat well, they are good insulators. Thus, Styrofoam with its trapped air is a good insulator.