Inertia is an intrinsic property of objects that causes them to resist changes in motion. It is this property that keeps objects in motion rather than momentum, as is commonly believed. Moments of inertia for just about every conceivable shape can be found in an appendix of a physics textbook, as well as on several websites.
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Experiments
A easy way to visibly examine the difference an object's shape has on its resistance to changes in motion is to roll objects down a ramp. There are two variables in determining the moment of inertia: an object's radius and its mass. Rolling two wheels of the same mass and radius -- one solid and one spoked -- down a ramp will demonstrate the difference the shape of a wheel has on its ability to accelerate, as the solid wheel has a smaller moment of inertia.
Density
Density has an effect on an object's inertia. You can demonstrate this by filling a jar with coins and another equal-size jar with sand until they both have the same mass. Rolling these two jars down a ramp will yield different speeds since their densities are not equal, yet their masses and radii are the same. Spinning a hard-boiled egg and a raw egg will produce different motions, as the liquid in the raw egg will cause it to wobble, while the consistency of the hard-boiled egg will make it spin smoothly.
Basketball and Tennis Ball
An interesting way of witnessing inertia in action is to drop a tennis ball and a basketball together. Try to position the tennis ball directly on top of the basketball so they hit the ground at the same time. Since the basketball has a much greater mass than the tennis ball, one might expect the basketball to bounce up "through" the tennis ball. What actually happens is the inertia of the basketball is transferred to the tennis ball upon impact with the ground, and the tennis ball bounces high in the air while the basketball stays on the ground.
Remaining at Rest
Inertia applies to objects that are not moving just as it does to objects in motion. Place an index card on top of a cup, and place a coin on the index card. Initially, the entire system -- the cup, index card and coin -- is at rest. Next, flick the edge of the index card with your finger to send the card in motion. The coin will drop harmlessly into the cup because its inertia keeps it in a state of rest and the force of friction between the coin and the index card is not sufficient enough to send it flying with the card.
Styrofoam and Aluminium Foil Experiments. Experiments present an opportunity for students to demonstrate basic scientific principles in a manner that can be...
