Friction and Gravity

Student vs. Forces Materials: Student The Teacher The student and teacher will stand face to face, with their palms of their hands touching. What happens if there is no movement? What happens if there is movement (acceleration) when one force is greater than the other? Draw what you see in your journal for each part.

Student Friction Pull Objective: Students will observe and discover how friction can cause an object/person to slow down. Materials: Student wearing socks A student wearing shoes Question: Which will create less friction: Pulling a student across the floor in shoes or socks? Make a prediction! Sketch what you see and write an explanation of why that happens.

Friction Friction is a force that is created whenever two surfaces move or try to move across each other. Friction can be useful and it can be harmful. Friction can be reduces by using lubricants such as oil, ball bearings, air cushions and wheels. Vehicles that are more steam-lined cause less friction as they move through the air. Friction produces heat. Friction results in wear and tear.

Gravity All matter has gravity. All matter pulls other matter towards its center. A pencil on the desk between two books will not move because gravity from both books is pulling with equal force. However the pencil is also pulling on both books. Since the forces are balanced, there is no movement. Movement of objects occurs when there is a force acting upon it. Example: Student pushing a pencil. The movement of the object is always toward the object with the greater mass. For example, when a pencil is thrown up in to the air, it goes up because a force is pushing it up. Eventually it will come down due to the greater mass of the Earth having more gravity.

Gravity Why do roots grown down? Why do cars roll down a ramp? Why do you slide down a slide? Why don’t you fall up?

HMH 152-155