The Nature of Forces

Forces Forces combined in the same direction are added. A force can cause an object to start moving, stop moving, or change direction. Forces combined in the same direction are added. Forces combined in opposite directions are subtracted

Balanced Forces Forces that are in opposite direction and equal in size. When forces are balanced there is no motion.

C. Unbalanced Forces Forces that are in the same direction or in opposite direction and unequal in size. When forces are unbalanced there is motion.

II. Friction A. Friction – Force that acts in the opposite direction of motion; will cause an object to slow down and finally stop

B. Sliding Friction When solid objects slide over each other Examples – Brakes Snow board

C. Rolling Friction Friction produced by objects such as wheels and ball bearings. Tends to be less than sliding friction. Examples – Wheels Ball bearings

D. Fluid Friction Friction when an object moves through fluids or gasses. Lubricants such as oil and grease change Sliding friction into fluid friction. Examples –Air resistance (terminal velocity), water resistance.

Desirable and Undesirable Friction *Brakes on a car *Soles on shoes Undesirable Friction *Moving parts in car engine *Air resistance

Newton's First Law of Motion An object at rest will remain at rest and an object in motion will remain in motion at constant velocity unless acted upon by an unbalanced force.

Inertia Tendency of objects to remain in motion or stay at rest unless acted upon by an outside force.

Second Law of Motion Shows how force, mass, and acceleration are related Force = Mass x Acceleration (F = m x a) Units – Newton (N) N = 1kg x 1m/s2

Third Law of Motion 1. States that for every action there is an opposite reaction. 2. For every force there is an opposite and equal force.

Gravity A. The acceleration of a falling object is due to the force of gravity between the object and earth.

Law of Universal Gravitation All objects in the universe attract each other by the force of gravity. The size of the force depends on the size of the masses and the distance between them.

Falling Objects Freefall - All falling objects accelerate at the same rate regardless of their masses. Acceleration due to gravity on earth is due to the force of gravity between the object and earth. (9.8 m/s2 ) For every second an object falls it will accelerate another 9.8 m/s. m = meters, s = seconds

5. Air Resistance Air resistance opposes motion, it is a type of fluid friction.

6. Terminal Velocity As an object falls air resistance gradually becomes equal to the pull of gravity, the object continues to fall but at a constant velocity.

Weight Weight is the measure of the force of gravity on an object. Weight = mass x acceleration due to gravity (w = m x g)

Weight 3. Units - Weight = N (Newton) Mass = kg (kilogram) Gravity = m/s2 (9.8 m/s2) 4. Newton = 1kg x 1 m/s2