Physics - Forces

How to make something move

Apply a force

Unit?

Newtons

1 Newton?

1 kg * m/s²

Newtons First Law

All objects will stay stationary or at constant velocity unless acted upon by an unbalanced force.

Unbalanced Forced?

Unequal forces. Force to the right 50 N and Force to the left is 30 N. So F_Net is not zero

Inertia

Habit of a body to remain at rest or in constant motion

Mass

Amount of matter in an object

Weight

The measure of gravity on an object

F_g = ?

F_g = ma

Force of Gravity equals Mass X Acceleration

Contact Forces

Forces applied by touch

Forces at a distance

Forces not applied by touch

Four fundamental forces of nature

1. Gravity

2. Electromagnetism

3. Weak Force

4. Strong Force

Newtons 2nd Law

The acceleration of an object depends directly on the net force and inversely on its mass

Acceleration

a = v₂ - v₁ / t

How to find F_Net

“Sum” all the forces on an object. Add the positives and subtract the negatives

Free Body Diagrams - FBD

A simplified way to show all the forces acting on an object, add arrows with all the forces on an object with labels, as well as a dot for the centre of mass. Does not include forces that the object applies

Newtons 3rd object

For every action there is an equal and opposite reaction

Action: Force of hand on desk

Reaction: Force of desk on hand

Action: Force of Cashmere on Ground

Reaction: Force of Ground on Cashmere

Action - Reaction Forces act on different Objects

F_n & F_g act on the same object

Normal Force

The reaction force to an object on a surface - always perpendicular to the surface - found by summing the forces on an object

Friction

The force between 2 sliding objects - directly proportional to normal force and roughness of object

Friction direction?

Opposite to direction of movement

F_fr = ?

Force of friction

F_fr = U_kF_N

Force of Friction = Coefficient of Kinetic force * Normal Force

U_k

Coefficient of Kinetic force

F_n

Normal Force

F_n & F_g

Are not always in opposite direction

Usually F_n is

The result of F_g pulling on an object and causing the object to touch and then apply a force to the surface

Static Friction

When a force is applied but the object stays at rest

When the object is at zero…?

….. The force of the static friction is equal to F_app

Maximum force required to over come static friction - GET THE OBJECT TO MOVE - Equation

F_fr = U_sF_N

U_s

Coefficient of static friction

When the object begins to move

the static friction turns to kinetic friction

When acceleration is = 0

F_N = mg

Your weight in Newtons changes in a moving elevator because..?

The equation for weight is impacted by acceleration due to gravity, which changes in a moving elevator