W HY IS IT EASY TO SLIP WHEN THERE IS WATER ON THE FLOOR ?

W HAT IS F RICTION ? Friction is a force that opposes motion between two surfaces that are in contact. Friction can cause a moving object to slow down and eventually stop.

W HAT C AUSES F RICTION ? Friction occurs because the surface of all objects are rough. Even surfaces that feel smooth are covered with microscopic hills & valleys. When two surfaces touch, the hills & valleys of one surface stick to the hills & valleys of the other.

W HAT A FFECTS F RICTION ? The force pushing the surfaces together. The larger the force pushing two surfaces together the more friction it will experience. The roughness of the surfaces. The rougher the surface of an object the more friction it will experience.

2 T YPES Kinetic Friction Friction that occurs between moving surfaces. Static Friction Friction that occurs between non-moving surfaces.

K INETIC F RICTION There are two types of kinetic friction: Sliding Friction Surfaces slide past each other. Rolling Friction One surface rolls over another surface. The force of sliding kinetic friction is greater than the force of rolling kinetic friction. So, it is usually easier to move objects on wheels than to slide objects along the floor.

S TATIC F RICTION With static friction the object does not move because the force of the static friction balances the force applied to the object. Static friction can be overcome by applying a large enough force. Static friction disappears as soon as an object starts moving, and then kinetic friction immediately occurs.

F RICTION : H ARMFUL & H ELPFUL Friction can cause things to wear out or erode. Friction also allows us to write and walk. Because friction can be both harmful and helpful, it is sometimes necessary to decrease or increase friction.

W AYS TO R EDUCE F RICTION Lubricants are substances that are applied to surfaces to reduce the friction between the surfaces. Examples: oil, wax, and grease. Switching from sliding kinetic friction to rolling kinetic friction. Making surfaces that rub against each other smoother.

W AYS TO I NCREASE F RICTION Making surfaces that rub against each other rougher. Increase the force pushing the surfaces together.

F RICTION ACTIVITY Imagine you have been asked to design a bowling alley/skating rink. You must describe 2 areas to reduce friction in the bowling alley/skating rink and 2 areas to increase friction in the bowling alley/skating rink. Make sure you explain why that area needs attention and describe what materials you will use to increase or decrease the friction for that area. Write in complete sentences.