Friction:The force that opposes motion between two surfaces that are in contact with each other. It causes objects to slow down or stop when they are sliding against each other.
Normal Force:The force exerted by a surface perpendicular (at right angles) to another surface that is in contact with it.
Acceleration:The rate at which an object changes its velocity over time. If you're speeding up or slowing down while sliding down a slide, you're experiencing acceleration.