Grade 6 Science: Force, Motion and Energy

Step 1: Your push to the right is an applied force.

Step 2: The floor rubs against the bottom of the box, pulling it back to the left: friction.

Step 3: Earth pulls the box down: gravity. That pull is the box’s weight.

Step 4: The floor pushes up on the box so it does not fall through: the normal force.

Step 1: The forces point in opposite directions, so subtract: 300 minus 250 is 50 newtons.

Step 2: The bigger force wins, so the net force is 50 newtons to the right.

Step 3: The net force is not zero, so the forces are unbalanced and the crate speeds up to the right.

Step 1: The swimmer pushes the water backward. That is one force, acting on the water.

Step 2: At the same instant, the water pushes the swimmer forward. That is the other force, acting on the swimmer.

Step 3: The two forces are equal in size and opposite in direction, so this is a Newton’s third law pair, and the swimmer moves forward.

Step 1: The ball on the shelf is high up: gravitational potential energy. The higher it is, the more it stores.

Step 2: The stretched rubber band: elastic potential energy, stored by stretching or squeezing.

Step 3: The granola bar: chemical potential energy, stored in the food and released when your body uses it.

Step 4: The rolling bike is moving: kinetic energy.

Step 1: At the top (A), almost all 100 joules is gravitational potential energy.

Step 2: At the bottom (B), the potential energy has become about 90 joules of kinetic energy, and friction has turned about 10 joules into thermal energy.

Step 3: Halfway up the next hill (C), there are about 50 joules of potential, 35 of kinetic and 15 of thermal energy.

Step 4: Add each one up: 100 joules every time. The energy changed form, but the total stayed the same.

Step 1: In the flashlight, the battery stores chemical energy. The circuit carries it as electrical energy, and the bulb turns it into light and some thermal energy.

Step 2: In nature, sunlight is light energy. Through photosynthesis, a plant stores it as chemical energy in sugar.

Step 3: A rabbit eats the plant and gets that chemical energy. Its body turns it into kinetic energy to hop and thermal energy to stay warm.

Step 4: In both systems, every bit of energy is still there: it was transferred or transformed, never destroyed.

Step 1: Shake a rope up and down. The rope moves up and down while the wave travels sideways along it. Movement at a right angle to the wave is a transverse wave.

Step 2: Push and pull the end of a stretched spring. The coils bunch up and spread out along the same line the wave travels. That is a longitudinal wave. Sound travels this way through air.

Step 3: In both, energy travels from one end to the other, but each bit of rope or coil ends up back where it started.