Chapter 9 Forces Lesson 1 Types of Forces

What is a Force? A force is any push or pull. When one object pushes or pulls another object the first object exerts a force on the second object.

And Because Science is in Love with Math… A force can be measured using the units of Newton.

Main Types of Forces Two main types of forces: Contact force Forces that act at a distance (non contact forces)

Contact Forces Contact forces are forces that directly come into contact with objects to apply a push or a pull. The main contact forces are: Applied force Normal force Friction

Contact Forces: Applied Force An applied force is a force that is put on an object by another object. Pushing or pulling a door open Pushing a friend, a shopping cart, a car Pulling a rope, some ones hair…

Contact Force: Normal Force A normal force is the force that acts between objects when they are in contact with each other perpendicular. (In science, normal in this context means perpendicular) Like a wall pushing back on you or the desk pushing back on your books or the Earth’s surface pushing back on your feet.

Contact Force: Friction Friction is a contact force that happens when two objects come into contact with each other and the surfaces exerts rub against one another.

Forces acting at a distance: Non Contact Forces Forces that act at a distance are forces that apply a push or a pull without ever touching. The following are all forces that push or pull but never touch the objects: Electrical force Magnetic force Gravitational force

Non contact force: electrical Electrical force is the force between two charged objects. This forces is expressed through atoms. Inside atoms are protons, neutrons and electrons. Protons are + positive charge Electrons are – negative charge Neutrons have no charge When same charge particles come into contact they repel each other. When opposite particles come into contact they attract.

Non Contact Force: Magnetic The attraction or repulsion between magnetic poles is called magnetic force.

Non Contact Force: Gravitational Gravitational force or gravity, is a force that pulls objects toward each other.

Law of Universal Gravitation The law of universal gravitation states that the force of gravity acts between all objects in the universe that have mass.

Factors that affect Gravity Two factors that affect the gravitational attraction between objects: Mass Distance

Factors that affect Gravity Mass and Distance affect gravitational pull between objects. The more mass an object has the greater the gravitational force between it and other objects will be. The closer the objects are the stronger the pull the farther away the weaker the pull of gravity on each other will be.

Factors that affect Gravity Distance also affects gravitational pull between objects. The closer objects are to each other the pull of gravity is greater. The farther apart they are the pull of gravity is less.

Mass vs. Weight Mass and weigh are related but are not the same thing. Mass is the amount of matter found in an object while weight is the measure of the pull of gravity on an object.