In grade 8, we talk about how force is equal to mass times acceleration. This means that the push on an object is related to how heavy it is and how much it is speeding up or slowing down. There is a lot of force behind an accelerating truck, but it is easy to absorb the force of a falling snowflake.
Eventually you will use computer programs that predict the motion of an object by calculating its speed and direction. For now, you need to memorize that motion is defined as an object’s direction and speed. Things that are moving have energy, and we call the energy of a moving object: kinetic energy. If you want to change the motion of an object, then you need a large mass and some force to push in the opposite direction.
One force is always slowing things down: friction. Friction makes a ball slow down as you throw it in the air. It also makes a sled slow down. Friction opposes motion.
Definitions that Virginia students are expected to know:
- motion: “object’s direction and speed”
- friction: “slows down motion”
- kinetic energy: “the energy of moving objects”
Ready to test your understanding?!?