In this hands-on activity, students are introduced to the concepts of static and kinetic friction and discover how the type of surface involved affects the strength of the frictional force. Prior to the activity, students discuss real life observations they have made illustrating friction at work (pushing an object across a rough surface, sliding on ice, etc.). The instructor may choose to pair this discussion with demonstrations, such as asking the students to push a heavy box across a slick surface, versus a carpeted surface. Discuss how kinetic friction is exerted on one surface by another when the two surfaces rub against each other because one or both of them is in motion. This frictional force is dependent on the type of surface as well as how hard the surfaces are pushing against each other. Students also learn that even when the object is not in motion, it is still being affected by static friction. One must exert a greater amount of force on the object than that which is being exerted by static friction in order to overcome it, causing the object in question to move. By understanding Newton’s laws, students may conclude that if you push or pull an object across a surface at a constant velocity, the force of friction is equal and opposite in direction to that of the push or pull.
Kinetic friction – The force of friction exerted on a surface as it rubs against another surface due to being in motion.
Static friction – The force exerted on a surface by another when neither surface is in motion. Maximum static friction is overcome when the object begins to move as a separate force is applied to it. Static friction acts in response to a force trying to cause it to move.
Newton’s Third Law – When an object exerts a force on another object, the second object exerts a force of equal strength and opposite in direction, back upon the first object.
This activity allows students with visual impairments to explore how the tactile qualities of different surfaces directly affect frictional force. The use of pennies as an informal metric of force is chosen due to ease-of-use, but a further extension/alteration could include the use of an adapted spring scale, of which is shown below. To observe the movement of the object across the different surfaces the student may be directed to place their hand at the edge of the surface, or lightly above it, feeling for the moment when the pull of the pennies exceeds that of maximum static friction and object is set into motion.