Work & Power
What unit is used to measure scientific work?
Joules (J).
A kickball rolls across the gym. What type of energy does it have because it is moving?
Kinetic energy.
What form of energy is stored in an apple before you eat it?
Potential Energy.
Energy moves from a hot mug to your hands. Is this an energy transfer or transformation?
Transfer. Energy moves from the mug to your hands.
Complete the law: Energy cannot be ______ or ______.
Created or Destroyed.
A student pushes a locked door, but it stays still. How much scientific work does the student do on the door? Explain.
0 J. The door does not move, so the distance is zero.
A student squeezes a spring and holds it still. What type of energy is stored in the spring?
Elastic Potential Energy.
An electric blanket warms up when plugged in. What form of energy increases as the blanket warms?
Thermal energy.
A plugged-in fan starts spinning. Is the change from electrical energy to the motion of its blades a transfer or transformation? Name the ending form.
Transformation. Electrical energy changes into kinetic energy as the blades spin.
A flashlight is turned off after being on for a while. The bulb is still warm. What form did some of the electrical energy change into?
Thermal energy. The warm bulb is evidence that some electrical energy changed into thermal energy.
A student pulls a wagon 5 m with a force of 9 N in the direction of motion. How much work does the student do?
45 J. Work = force × distance = 9 N × 5 m.
Two identical backpacks are at rest. One is on a chair and the other is on the floor. Which has more gravitational potential energy relative to the floor, and why?
The backpack on the chair. Both have the same mass, but the one on the chair is higher.
In one reaction, a large nucleus splits apart. In another, small nuclei join together. Name both reactions in order.
Nuclear Fission and Nuclear Fusion
A rolling soccer ball hits a still ball. The second ball starts rolling. Which ball gives energy, which receives it, and what is the evidence?
The first ball transfers energy to the second ball. The evidence is that the second ball starts moving after the collision.
A student rubs their hands together and feels them become warmer. Which energy transformation best explains this?
Kinectic energy to Thermal energy.
A motor does 240 J of work in 8 seconds. What is its power?
W. Power = work ÷ time = 240 J ÷ 8 s.
An empty wagon and a loaded wagon roll at the same speed. Which has more kinetic energy, and why?
The loaded wagon. At the same speed, the wagon with greater mass has more kinetic energy.
What moves in an electric current through a wire? How does light from the Sun travel to Earth?
Electric charges move through the wire. Sunlight travels as electromagnetic waves that can move through empty space.
Sunlight travels to a blacktop playground. The blacktop absorbs the sunlight and gets warmer. Which part shows energy transfer, and which part shows energy transformation?
Transfer: Energy travels from the Sun to the blacktop. Transformation: The blacktop absorbs electromagnetic radiation(Sunlight), which changes into thermal energy.
A tennis ball bounces lower each time. A student says the missing energy was destroyed. How would you respond?
Some of the ball’s gravitonal potential energy becomes Kinectic energy and sound.
Motor A does 300 J of work in 5 seconds. Motor B does 420 J in 7 seconds. Which motor has more power? Show how you know.
They have the same power. Motor A: 300 ÷ 5 = 60 W. Motor B: 420 ÷ 7 = 60 W.
A playground swing moves from its highest point toward the bottom. How do its gravitational potential energy and kinetic energy change, and where is its kinetic energy greatest?
Gravitational potential energy decreases as height decreases. Kinetic energy increases as speed increases. Kinetic energy is greatest at the bottom, where the swing moves fastest.
A student eats an apple, runs a lap, and feels warmer afterward. Name the starting form of energy and the two forms you can identify from the student’s motion and warmth.
Chemical energy is stored in the apple. Some becomes kinetic energy as the student runs, and some becomes thermal energy as the body warms.
An electric kettle heats water. Identify one energy transformation in the heating element and one energy transfer to the water.
Transformation: Electrical energy changes into thermal energy in the heating element. Transfer: Energy moves from the hot element to the water, warming it.
Before soccer practice, a player eats a granola bar. Later, the player runs up to a still soccer ball and kicks it. Where was the chemical energy stored, how did the player gain kinetic energy, and how did the ball gain kinetic energy?
Chemical energy was stored in the granola bar. The player’s muscles used some of that energy to move, giving the player kinetic energy. During the kick, the player’s foot transferred energy to the ball, giving it kinetic energy as it rolled away.