Middle school year 3 · fourth unit
Motion and Energy
Say fast and slow in numbers, measure how a falling object speeds up, and work out the energy of an object held high. Put motion into numbers and graphs and you can know in advance even what you have never seen.
An escalator always moves at the same rate
A board to runWhat does going at a steady rate look like on a graph? Take the car, pull it back to the left and let go.
Drop a bowling ball and a marble together
A board to runIt seems the heavy one should land first. Drag the gold bar to set the height and let go.
Lifting a heavy load high takes effort
A board to adjustWhere did that effort go? Drag the box up onto a shelf, then tap it to push it off.
A roller coaster has no engine
A board to adjustHaul it up once at the start and it runs to the end. Take the cart and set it on the track.
What to take away from this unit
- Speed is distance divided by time. Motion at an unchanging speed is uniform motion, and its graph of distance against time is a straight line.
- Falling under gravity alone is free fall. The speed grows steadily by 9.8 m/s every second, and objects of different mass fall alike.
- In science, work is moving an object in the direction of the force applied. Work = force × distance, in J (joules). Push without moving anything and the work is zero.
- Energy is the ability to do work. An object held high has potential energy (9.8 × mass × height); a moving object has kinetic energy (½ × mass × speed²).
- Potential and kinetic energy change into each other. With no friction or air resistance, their sum (mechanical energy) does not change.