FORCE is any push or pull which causes

FORCE is any push or pull which causes something to move or change its speed or direction

What is Force? • Force is the capacity to do work or cause physical change • Forces have both size and direction • Force = mass x acceleration • Force is measured in Newtons (N) – N = (kg. m/s 2). • Forces are measured using a spring scale.

Types of Forces 1. Contact Forces: a push or a pull on one object by another object that is touching it. Ex. friction, air resistance, tension, normal, applied, spring 2. At a Distance/Noncontact Force: a force that one object can apply to another object without touching it. Ex. Gravity, Electric, Magnetic

What is friction? • A force that resists the motion of two surfaces that are touching. It causes heat, damage, wear, and slowing.

What is friction? • Types of friction: – Static Friction: static means having no motion. – Sliding Friction: occurs when a force is great enough to overcome the static friction.

What is rolling friction? • Rolling friction is the friction which enables wheels to turn, helping objects to move. • If there were no rolling friction, turning wheels would not enable an object to move.

What is fluid friction? • Fluid friction is friction between a surface and a fluid. • A fluid is any material that flows therefore, water and air are both fluids. • Fluid friction between air and a surface is air resistance.

What causes friction? • There are two factors which affect friction between two surfaces: – Kind of surfaces in contact (rough or smooth) – Amount of force pressing the surfaces together. The rougher the surface and the stronger the force between the surfaces, the greater the amount of friction.

Reducing Friction • Lubricant: oils, grease, and soap • Streamlining (aerodynamics) • Making surfaces rougher ·Smoothing surfaces

Friction … Pros and Cons PROS • Enables us to stand move without falling • Makes a pencil work • Need friction for tires to move a car CONS • Causes engine parts to wear out • Causes holes in your socks • Causes wind and water erosion

What is tensional force? • A force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends.

What is normal force? Normal force is the support force exerted upon an object which is in contact with another stable object. Example: If a book is resting on a table, the table is exerting a normal force on the book in order to support the weight of the book.

What is applied force? An applied force is a force which is applied to an object by a person or another object.

What is spring force? Spring force is the force exerted by a compressed or stretched spring upon any object which is attached to it.

What is Gravitational force? • Gravity is a force of attraction between two objects. • Gravity is an “at a distance” force • Law of Gravitation – any two objects exert an attractive force on each other. The amount of attraction depends upon two things: the mass of the objects and the distance between the objects.

What is electrical force? Electrical force is created by attraction of positive and negatively charged particles

What is magnetic force? Magnetic force is the attraction or repulsion between electrically charged particles because of their motion.

Forces can be BALANCED or UNBALANCED l Balanced forces are equal in size and opposite in direction l Unbalanced forces are not equal in size and/or opposite in direction. If the forces on an object are UNBALANCED, we say a NET force results. This will result in a change in motion!!

Net Force = Combination of all forces acting on an object. Fnet Ffriction Fpull N W N

Balanced Forces üNet force = 0 üNo change in motion üNo change in direction. üObject either at rest or moving at a constant velocity.

Unbalanced Forces üNet force is ≠ 0 üChange in motion üChange in direction. üObject’s motion or direction of motion changing.

Determine the NET FORCE:

FN Fg

unbalanced versus balanced test yourself

Net Force Problems Need to know amount of forces and their direction. Use free-body diagrams to calculate net force. Net force = the sum of all the forces acting on an object.

Practice Problems Problem 1 Problem 2 A book is at rest on a table top. An egg is falling from a nest in a tree.