F = maA force is a push or pull upon an object resulting from the object's interaction

with another object.

Force is always measured in NewtonsN= kg·m/s2

Indirect or at-a-distance forces: Gravitational force – always present

between two objects that have mass. Usually not felt unless one of the objects is very large. On earth 9.81 m/s2. Always pulls down.

Magnetic force Electrical force

Direct or Contact forces:

Normal force: force on an object in contact with another stable object. Always perpendicular to the surfaces in contact.

Weight of block

NormalForce

FrictionForce

Direct or Contact forces:

Applied force: a force applied to one object by another.

Frictional force: The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it.› Sliding friction: between moving objects› Static friction: between stationary objects› Air resistance

Direct or Contact forces:

Tension: the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends.

Spring force: exerted by a compressed or stretched spring upon any object that is attached to it.

Free body diagrams

Force is a vector. Force vector arrows are drawn in the direction that the force is pushing or pulling.

A student pushes a box across the floor with an acceleration of 1.0 m/s2. Diagram this situation.

A backpack is at rest on a chair. Diagram the forces acting on the chair.

A skydiver is free falling at terminal velocity. Draw a free body diagram showing this situation.

A sign is hanging from two ropes. Draw a diagram representing this situation.

Go Zebras!

FtFt

Fg