Calculating Friction

Goals:

I can calculate normal force and force of friction.

I can determine the coefficient of friction between two surfaces.

To understand and reduce friction, you have to be able to measure it. Every pair of surfaces has a measurablecoefficient of frictionthat helps engineers identify and control friction in systems. Begin by watching the Friction video and then investigate the friction that various surface pairs create.

Table showing several common coefficients of friction.

Practice problems. Show all work on paper when you submit please!

1. Calculate the force of friction acting on a 10 kg rubber block sliding on a concrete floor (=0.65).

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1. Calculate the force of friction acting on an 8 kg wooden box sliding on a leather-covered desk. (=0.40)

1. Calculate the force of friction acting on a 37 kg wooden crate sliding across a wood floor. (=0.20)

1. An ice skater is using steel ice skates to glide across a frozen pond. She pushes off with the force of 80N. What is her force of friction acting against her?

1. The bones in our joints are lubricated by a fluid called 'synovial fluid' that reduces friction. It has a kinetic coefficient of friction of 0.015. If you are moving your shoulder joint with a force of 8N, what is the force of friction acting against your joint?

1. A Ferrari Testarossa can accelerate up to a rate of 24 m/s². It has a mass of 1700 kg. It has a kinetic coefficient of friction of 0.37. If it is accelerating at its highest rate, what is the force of fluid friction by wind resistance?

1. When rubber shoes slide against a concrete floor, they have a coefficient of kinetic friction of 0.7. If the force of friction that is produced is 10N, what is the normal force?

1. Two oiled steel parts produce friction inside of a car engine. The force of friction produced is 0.6N, and the normal force causing them to interact is 20N. What is the coefficient of friction of the two oiled steel parts?

1. A parachute is released when a person goes skydiving. The coefficient of kinetic friction of the parachute is 0.75. The person is experiencing friction, in the form of wind resistance, of 236.25N. The normal force of the person falling is 315.00N. The person weighs 67 kg. What is the acceleration (m/s²) of their bodies towards earth?

1. A 100 N force is applied to the side of a crate resting on a level floor. The crate has a mass of 50 kg. If the coefficient of static friction is s = .25, is the 100 N force enough to make the crate accelerate? Explain why or why not. N =F = ma (a= 9.81 m/s2)

1. A car has a coefficient of friction between the ground and its tires of .85. What is the mass of the car if it takes 9620 N of force to make it slide along the ground? (a= 9.81 m/s2)

1. A box takes 350 N to start moving when the coefficient of static friction is .35. What is the weight of the box?

1. What is the coefficient of static friction if it takes 34 N of force to move a box that weighs 67 N?

1. A 9.6 kg object is pulled along a horizontal surface. If the coefficient of friction is 0.11 what is the force of friction? (a= 9.81 m/s2)