Forces Friction b Forces Definition of a Force

Forces & Friction b. Forces

Definition of a Force b. A lift, pull or push that gives energy to an object, sometimes causing it to start moving, stop moving or change direction.

Balanced Force b A force that produces no change in an object’s motion because it is balanced by an equal, opposite force.

Unbalanced Forces b. A force that results in an object’s motion being changed. +

Friction b. A force that acts in a direction opposite to the motion of the moving object.

Friction b. Friction causes an object to slow down and stop.

Static Friction b. Friction that tends to keep an object at rest

Sliding Friction • Occurs when objects slide over one another

Rolling Friction b. Produced by rolling objects, such as wheels or ball bearings It occurs between the wheels and the floor

Fluid Friction b. It is exerted on an object by fluids, slowing the object down

Newton’s 1 st Law of Motion b. Object in motion stays in motion

Newton’s 1 st Law of Motion b. Object at rest stays at rest

Newton’s 1 st Law of Motion b. As long as the forces acting on an object are balanced the object does not change its motion.

Inertia b Tendency for an object to stay at rest or moving in a straight line at a constant speed.

Unit of Force b Unit of mass is kg b Unit of Acceleration is m/s/s b 1 kg x 1 m/s/s = 1 kg x m/s/s = 1 Newton (N) b Resulting in Force unit called a Newton (N)

Newton’s 2 nd Law of Motion Force = Mass X Acceleration F=ma Force Mass Acceleration

Newton’s 2 nd Law of Motion b. The greater the mass of an object, the greater the force required to change its motion.

Newton’s 2 nd Law of Motion b The greater the acceleration of an object, the greater the force required to change its motion.

Newton’s 3 rd Law of Motion b For every force there is an equal and opposite reaction by another force

Newton’s 3 rd Law of Motion b. All forces come in pairs b Examples: • Person walking

Newton’s 3 rd Law of Motion Standing on a scale b

Newton’s 3 rd Law of Motion Rowing a boat b

Newton’s 3 rd Law of Motion b. Bird flying

Universal Law of Gravitation b. All objects in the universe attract each other by the force of gravity

Universal Law of Gravitation Gravity 1) the mass of the varies object doing the depend pulling, and ing on 2) the distance from two the center of that factors: object

Universal Law of Gravitation b. On Earth gravity = 9. 8 m/s/s b. For every second that an object falls its speed increases by 9. 8 m/s

Universal Law of Gravitation b. The acceleration due to gravity may be affected by the air resistance of the falling object.

Universal Law of Gravitation Objects that have a large surface area and a small mass will fall much slower than objects with a small surface area and large masses

Weight b. Weight = Mass X Gravity b. Unit of mass = kg b. Unit of gravity = m/s/s b. Unit of weight = Newton

Formula for Weight Mass Gravity