How do science concepts apply to your world? Here are some questions you'll be able to answer after you read this chapter.

• Why doesn't the pulling by each team in a tug of war always result in motion?
• Why do flying squirrels spread their arms and legs when they jump through the air?
• What happens to the forward motion of a passenger in a head-on auto accident?
• What brings the head of a hammer to a stop when you drive a nail into a board?
• What causes tides?
• What factors affect the fall of a sky diver?

What Starts an Object Moving?

Procedure

1. On a flat surface, arrange four pennies in a row so that they are touching one another.
2. Using your index finger, slide a fifth penny across the surface in line with the row of pennies so that it strikes a penny at one end of the row.

Think About It

1. Observing   Describe how the row of pennies moves in response to the collision.
2. Formulating Hypotheses   What do you think caused the pennies to move after the collision? Why didn't the pennies move before the collision?