Exploring Inertia by Rachel Goodfriend

Rachel Goodfriend
Exploring Inertia Lab: Using Scientific Methods
8th Grade Physical Science

Principles Investigated:
    Students will learn that inertia is a property of all matter, from small particles of dust to enormous planets and stars.  Students will observe several effects of inertia and describe how balanced and unbalanced forces affect the motion of objects.

California Content Standards:
    8.2c.  Students know when the forces on an object are balanced, the motion of the object does not change.
    8.2e.  Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).

    -egg, hard boiled
    -egg, raw
    -card, index
    -cup, plastic

Station 1:  Magic Eggs
1.  Ask a Question:  There are two unmarked eggs at this station.  The masses of the two eggs are about the same.  Without breaking them open, how can you tell which egg is raw (liquid inside) and which egg is hard boiled (solid all the way through)?
2.  Form a Hypothesis:  Before you do anything to either egg, make some predictions.  Will there be any difference in the way the two eggs spin?  Which egg will be easier to stop?
Test the Hypothesis:
3.  First, spin one egg.  Then, place your finger on it gently to make it stop spinning.  Record your observations.
4.  Repeat step 3 with the second egg.
5.  Compare you predictions with your observations.
6.  Which egg is hard boiled and which egg is raw?  Explain.

Station 2:  Coin in a Cup
1.  At this station, you will find a coin, an index card, and a plastic cup.  Place the card over the cup.  Then, place the coin on the card over the center of the cup, as shown below.
2.  Write down a method for getting the coin into the cup without touching the coin and without lifting the card.
3.  Try your method.  If it doesn’t work, try again until you find a method that does work.

Student Prior Knowledge:
  • Students must know that a force is a push or a pull exerted on an object, that balanced forces cause no change in motion, and unbalanced forces cause a change in velocity of an object.
  • Students must know that friction is a force that opposes motion between two surfaces that are touching.  Friction is a force that can balance other forces to prevent motion, or when unbalanced, can change the velocity of an object.
  • Students must have prior knowledge in using scientific methods like asking a question, forming a hypothesis, testing a hypothesis, analyzing and evaluating results, drawing and defending conclusions, and applying conclusions.           
  • Students must know that inertia is the tendency of an object to resist a change in motion.
  • Students must know that velocity is the speed of an object in a particular direction.
  • Students must know that mass is a measure of the amount of matter in an object.
  • Students must know that acceleration is any change in velocity over time.

Question & Answer:
Station 1: Magic Eggs
1.  Explaining Events:  Explain why the eggs behave differently when you spin them even though they should have had the same inertia. (Hint: Think about what happens to the liquid inside the raw egg.)
2.  Drawing Conclusions:  Explain why the eggs react differently when you try to stop them.

Station 2:  Coin in a Cup
1.  Describing Events:  use Newton’s first law of motion to explain why the coin falls into the cup if you remove the card quickly.
2.  Defending Conclusions:  Explain why pulling on the card slowly will not work even though the coin has inertia.  (Hint:  Friction is a force.)

Station 1 & 2:
1.  Applying Conclusions:  Both moving and non-moving objects have inertia.  Explain why throwing a bowling ball and catching a thrown bowling ball are hard.
2.  Evaluating Results:  Explain your observations in the lab in terms of balanced and unbalanced forces.  When were the forces on the object balanced?  What happened when the forces became unbalanced?

Applications to Every Day Life:

Students can not only apply Newton’s laws of motion to their every day life, but to their future careers as well.  For my students interested in space exploration, it is important to know that astronauts must remember Newton’s first law of motion when they are training to work in a so-called weightless environment.  Weightless objects still have plenty of inertia and require a significant amount of force to change their motion.  The laws of motion have helped NASA scientists to develop training procedures that all astronauts undergo before space travel, in particular the KC-135 airplane or “Vomit Comet” which simulates what it feels like to orbit earth in a space shuttle.

    For my students interested in pursuing careers in environmental science, having knowledge of Newton’s laws of motion is important in designing cars.  On average, older cars pollute the air more than newer cars do and one reason is that older cars may have more mass than newer cars.  From Newton’s second law, students learn that a small car with a small engine can still have good acceleration and use less fuel.
    For my students interested in marine biology, Newton’s third law of motion can help them understand how a squid propels itself through the water.   For students interested in engineering, knowledge of Newton’s laws is important for building bridges, designing roller-coasters, and robotics technology.

California Physical Science by Holt, Rinehart & Winston, a Hartcourt Education Company.  2007.
Norman Herr,
Dec 1, 2010, 6:53 PM