Forces 3.1

Mass - amount of matter in an object Review Vocabulary Mass - amount of matter in an object

What is force? A force is a push or a pull. Applied force changes the movement. Sometimes, it is obvious that a force has been applied. But other forces are not as noticeable. ©Lawrence Manning/Corbis

The force of the moving ball causes the ball at rest to move in the direction of the force.

Net Force When two or more forces act on an object at the same time, the forces combine. This is called a net force. Forces on an object that are equal in size and opposite in direction are called balanced forces. The net force is zero. Net Force =0

+ What is the result of unbalanced forces? Net Force = When the forces are not balanced, the net force that moves the object is the difference between the two forces. + Net Force =

unbalanced forces The forces combine, or add together, because they are exerted in the same direction. The net force is equal to both forces added together. + Net Force =

Friction is the force that opposes the sliding motion of two surfaces that are touching each other.

The amount of friction between two surfaces depends on: The kind of surfaces that are touching. The amount of force that is pressing the surfaces together.

What Causes Friction? Friction is caused by the microwelds that form where the surfaces are in contact.

What makes things stick together? The greater the force pushing two surfaces together, the stronger the microwelds will be. To move one surface over another, a force must be applied to break these microwelds.

Types of Friction

Types of Friction Definition - Caused by: Examples: Definition - In your notebook, make a graphic organizer for the 3 types of friction. For each type give a definition, state why it is caused by, and give at least 2 examples of that type. Types of Friction Definition - Caused by: Examples: Definition - Caused by: Examples: Definition - Caused by: Examples:

Static friction is the force that keeps two surfaces at rest from sliding across each other. Caused when the force is not large enough to break the microwelds

Sliding friction is the force that works against the motion of two surfaces that are sliding across each other. caused by the microwelds breaking and then forming again

Rolling friction is the frictional force between a rolling object and the surface it rolls on. Caused when the object and surface are deformed at their point of contact