All About Forces

http://www.youtube.com/watch?v=HK8afQRrOck

Forces

General Characteristics: They are vectors Push or Pull Units = Newtons, Pounds

Newton = force required to accelerate 1 kg at a rate of 1 m/s²

Nature of Forces

Forces exist in pairs (its impossible for a single force to act on an object)

Forces arise as a result of actions / reactions between objects

There are always forces acting on all objects

***There are 4 fundamental forces** Gravitational, electromagnetic, strong

nuclear, weak nuclear

Classification Of ForcesContact & Long-Range & Short Range

Contact: Frictional

Force Applied Force Normal Force Tension Force

Long Range: Gravitational Electromagnetic

Short Range: Strong Nuclear Weak Nuclear

Gravitational Force

Weakest of all forces Only noticed when one object is

massive Acts over infinite distances

Electromagnetic Force

Can be repulsive or attractive

Acts between objects with an electrical charge

Holds atoms and molecules together

Strong Nuclear Force

Strongest of all forces Only acts over distances comparable

to the size of an atom The force that holds protons and

neutrons together

Weak Nuclear Force

Also acts over small distances Involved in radioactive decay

We will study gravitational & electromagnetic forces later on…

Drawing Free Body Diagrams

A book is at rest on a tabletop.

Drawing Free Body Diagrams

A girl is suspended motionless from the ceiling by two ropes.

Drawing Free Body Diagrams

An egg is free-falling from a nest in a tree. Neglect air resistance.

Drawing Free Body Diagrams

A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance.

Drawing Free Body Diagrams

A car is coasting to the right and slowing down.

Drawing Free Body Diagrams

A force is applied to the right to drag a sled across loosely packed snow with a rightward acceleration.

Newton’s 3 Laws of Motion

#1 = Objects at rest stay at rest, objects in motion stay in motion (unless acted on by an outside force).

Inertia Tendency of an object to resist change http://www.youtube.com/watch?v=--

MDILG7Znk

Net Force and Equilibrium

The net force is the vector sum of all the forces that act upon an object When forces are Unbalanced

Equilibrium If the net force on an object is

Zero Object is either at rest or a

constant velocity

Determine the missing forces