Newtons 3 rd Law More Practice Newtons 3

An Introduction to Friction: Student Learning Goal Students will be able to perform an

Weight Recall that the gravitational force acting on an object is also called the

The Normal Force Recall that the normal force is the force acting to keep

FN not equal to Fg If there is a vertical applied force, the normal

FN not equal to Fg Example A 5 kg book is resting on the

Direction of FN Note that the normal force is always perpendicular to the surface.

Friction Recall that friction is the force acting to oppose any (attempted) motion and

Mu The magnitude of the frictional force is given by:

Mu The magnitude of the frictional force is given by: where (mu) is the

Mu Examples E. g. ● For steel on wood, (kinetic) = 0. 25 k

Example Problem A 1200 -kg car without ABS brakes is skidding on dry concrete.

ABS Brakes If the car does have ABS brakes, the car’s tires will continue

More Practice Static and Kinetic Friction Lab

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Newton’s 3 rd Law: More Practice

An Introduction to Friction: Student Learning Goal Students will be able to perform an investigation to determine the factors affecting static and kinetic friction, and to determine the corresponding coefficient of friction between an everyday object and the surface with which it is in contact. (C 2. 3)

An Introduction to Friction SPH 4 C

Weight Recall that the gravitational force acting on an object is also called the weight.

Weight Recall that the gravitational force acting on an object is also called the weight. Its magnitude is equal to: where m is mass, measured in kg, and g = 9. 8 m/s 2.

Weight Recall that the gravitational force acting on an object is also called the weight. Its magnitude is equal to: where m is mass, measured in kg, and g = 9. 8 m/s 2. Weight is therefore measured in Newtons.

The Normal Force Recall that the normal force is the force acting to keep objects apart.

The Normal Force Recall that the normal force is the force acting to keep objects apart. For an object on a horizontal surface with no vertical applied force, the normal force will be equal to _____. FN e. g. a box pushed rightward across a table Ff FA Fg

The Normal Force Recall that the normal force is the force acting to keep objects apart. For an object on a horizontal surface with no vertical applied force, the normal force will be equal to the weight. FN e. g. a box pushed rightward across a table Ff FA Fg

The Normal Force Recall that the normal force is the force acting to keep objects apart. For an object on a horizontal surface with no vertical applied force, the normal force will be equal to the weight (since the vertical forces must balance). FN e. g. a box pushed rightward across a table Ff FA Fg

FN not equal to Fg If there is a vertical applied force, the normal force will not equal the weight. Example A 5 kg book is resting on the table. If Selma is pushing down on the book with a force of 20 N, what is the normal force the table is exerting on the book?

FN not equal to Fg Example A 5 kg book is resting on the table. If Selma is pushing down on the book with a force of 20 N, what is the normal force the table is exerting on the book? FN = ? FA= 20 N Fg=(5 kg)(9. 8 m/s 2) = 50 N

Direction of FN Note that the normal force is always perpendicular to the surface. If the surface is vertical (e. g. a magnetic board to which a magnet is attached), the normal force must be horizontal.

Friction Recall that friction is the force acting to oppose any (attempted) motion and is therefore always opposite in direction to the attempted motion. The magnitude of the force of friction will depend on the properties of the surfaces in contact

Mu The magnitude of the frictional force is given by:

Mu The magnitude of the frictional force is given by: where (mu) is the coefficient of friction, determined by the properties of the surfaces in contact.

Mu The magnitude of the frictional force is given by: where (mu) is the coefficient of friction, determined by the properties of the surfaces in contact. is dimensionless (no units) and is ≤ 1 (approx. ).

Mu Examples E. g. ● For steel on wood, (kinetic) = 0. 25 k s (static) = 0. 45 Note that s > k : it’s harder to get things moving than keep things moving.

Mu Examples E. g. ● For steel on wood, (kinetic) = 0. 25 k s (static) = 0. 45 ● For steel on ice, (kinetic) = k s (static) =

Mu Examples E. g. ● For steel on wood, (kinetic) = 0. 25 k s (static) = 0. 45 ● For steel on ice, (kinetic) = 0. 010 k s (static) = 0. 10 ● For rubber on dry concrete, (kinetic) = k s (static) =

Mu Examples E. g. ● For steel on wood, (kinetic) = 0. 25 k s (static) = 0. 45 ● For steel on ice, (kinetic) = 0. 010 k s (static) = 0. 10 ● For rubber on dry concrete, (kinetic) = k 1. 0 s (static) = 1. 1

Example Problem A 1200 -kg car without ABS brakes is skidding on dry concrete. What is the magnitude of the force of friction acting on the car?

ABS Brakes If the car does have ABS brakes, the car’s tires will continue to roll and grip the road while stopping and the relevant coefficient will be that of static friction:

ABS Brakes If the car does have ABS brakes, the car’s tires will continue to roll and grip the road while stopping and the relevant coefficient will be that of static friction: i. e. there is more force stopping the car when the tires are rolling and not sliding

More Practice Static and Kinetic Friction Lab