Physics Unit 3 - Force

Force

A push or a pull

Inertia

An object’s resistance to a change in motion

Friction

A force that opposes the relative motion (or attempted motion) between two surfaces in contact. It always opposes the direction of motion or the tendency to move.

Acceleration & Mass Relationship

Inverse, a = 1/m, decreasing curve

Acceleration & Force Relationship

Direct, a = kf, increasing linear

Newton’s First Law of Motion

An object at a constant velocity will stay at that constant velocity unless acted upon by an outside force

Newton’s Second Law of Motion

F = ma

→ acceleration is caused by a force, in direction of force, directly related to force, indirectly proportional to mass

Newton’s Third Law of Motion

For every action force there is a reaction force equal in magnitude and opposite in direction

What do Newton’s Three Laws of Motion do?

They relate force to motion

Mass

• Amount of matter a body contains

• Measurement of Inertia

• Measured with a balance

• Amount does not change

• Measured in kg (kilograms)

Weight

• A force

• The force of gravity (the force of the earth) pulling on an object

• Measured with a scale

• Amount changes with respect to where you are

• Measured in N (Newtons)

Terminal Velocity

When the force of air resistance = the weight of the object (the force of gravity)

Net Force

F_net ; the vector sum of fall forces acting on an object (ex: F_netx = sum of all horizontal forces - F_f)

Normal Force

F_N ; support force that is always perpendicular to surface an object is on

Friction Force

F_f = always resists movement and is in direction opposite of motion

F_f = μ * F_N

Coefficient of Friction

μ

Tension

T, force in a rope (or string, chain, etc)