Thought Experiments and Numbers: teacher key

Pushes and Pulls, grade 8 edition, written for 8th grade. Galileo used ramps and a thought experiment to study falling and motion. See the numbers behind free fall, skydivers, friction and the Apollo 15 hammer and feather.

Read the book. Print this page for the key.

Questions and answers

1. Fall for twice as long, and how far does a ball drop?
   • Twice as far
   • Three times as far
   • Four times as far (answer)
2. Why could a heavy body joined to a light body not both fall faster and slower?
   • Light bodies cannot fall
   • The light one should slow the heavy one, yet the pair should fall faster (answer)
   • The pair has no weight
3. What happened to the hammer and feather in the Apollo 15 test?
   • They struck the surface at about the same time (answer)
   • The feather landed first
   • The hammer landed first
4. Which skydiver reaches terminal velocity at a higher speed in the textbook example?
   • The 100-kilogram skydiver
   • Both reach the same speed
   • The 150-kilogram skydiver (answer)
5. What is a fulcrum?
   • The fixed point where a lever pivots (answer)
   • A kind of ramp
   • A unit of force
6. A crate is already sliding. Compared with starting it, how much push keeps it moving at constant speed in the example?
   • More push
   • About the same push
   • Less push (answer)

Words

• inertia: resisting change
• momentum: mass times velocity
• fulcrum: lever's pivot point
• projectiles: thrown objects