Chapter Menu Lesson 1: Combining Forces Lesson 2: Types of Force Lesson 3: Unbalanced Forces and Acceleration Click on a hyperlink to view the corresponding lesson.

2.1 Combining Forces force contact force noncontact force net force unbalanced forces balanced forces Newton’s first law of motion

2.1 Combining Forces Force When more than one force acts on an object, the combined effect is caused by the sum of all applied forces. A push or a pull on an object is a force.

Contact and Noncontact Forces 2.1 Combining Forces Contact and Noncontact Forces A contact force is exerted only when two objects are touching. A noncontact force is exerted when two objects are not touching. Magnets exert a noncontact force on each other.

Force is a Vector Vectors have magnitude and direction. 2.1 Combining Forces Force is a Vector Vectors have magnitude and direction. Force has a direction and a magnitude. Force is measured in Newtons.

2.1 Combining Forces Combining Forces When more than one force acts on an object, the forces combine. The combination of all the forces acting on an object is called the net force.

Combining Forces in the Same Direction Forces are vectors and require a reference direction. When forces in the same direction combine, the net force is in the same direction and the size of the force is the sum of the forces.

Combining Forces in the Same Direction (cont.) If two people push the dresser to the right, the forces are added together.

Combining Forces in Opposite Directions When forces in opposite directions combine, the net force is in the direction of the larger force. The size of the net force is the difference between the two forces.

Combining Forces in Opposite Directions (cont.) Two people exerting a force in opposite directions show how vectors combine to create net force.

Unbalanced and Balanced Forces 2.1 Combining Forces Unbalanced and Balanced Forces If the net force on an object is not zero, it is an unbalanced force. If the net force on an object does equal zero, it is a balanced force.

2.1 Combining Forces Balanced Forces

Balanced Forces and Motion 2.1 Combining Forces Balanced Forces and Motion If two people push with the same force, the door does not move. The forces have the same magnitude. The forces are in opposite directions. The net force on the door is zero and the forces are balanced. The motion of the door does not change.

Unbalanced Forces and Motion 2.1 Combining Forces Unbalanced Forces and Motion Unbalanced forces change motion. If two people push with different force, the door moves. The forces have a different magnitude and are in opposite directions. The net force on the door is not zero and the forces are unbalanced. The door moves in the direction of the larger force.

Newton’s First Law of Motion 2.1 Combining Forces Newton’s First Law of Motion If the net force on an object is zero, the velocity of the object does not change. If the net force is zero and the object is at rest, it remains at rest. If the net force is zero and the object is moving, it continues to move in a straight line with constant speed. Newton’s Laws of Motion

Inertia and Mass Mass is the amount of matter in an object. 2.1 Combining Forces Inertia and Mass Mass is the amount of matter in an object. The size of the net force needed to cause a certain change in motion depends on the object’s mass. A bicycle is easier to push than a car because it has less mass.

2.2 Types of Forces gravity law of universal gravitation weight friction elastic force tension force compression force normal force

Gravity Many types of forces act on objects. Gravity is an attractive force between all objects that have mass.

2.2 Types of Forces Gravity (cont.) The ball does not travel in a straight line because of the unbalanced force of gravity acting on it.

The Law of Universal Gravitation 2.2 Types of Forces The Law of Universal Gravitation The Law of Universal Gravitation states that all objects with mass are attracted to each other. The magnitude of attraction depends on the mass of each object and the distance between them.

The Law of Universal Gravitation (cont.) 2.2 Types of Forces The Law of Universal Gravitation (cont.) The gravitational force becomes stronger as either or both objects increase in mass. The gravitational force becomes weaker as the distance between the objects increases.

2.2 Types of Forces Weight and Mass Mass is the amount of matter in an object and does not change with location. Weight is the gravitational force on a object and changes with location. Weight is a force and a vector. Weight changes with height above Earth.

2.2 Types of Forces Friction Friction is a force that opposes the movement between two surfaces in contact. A book pushed across a table slows down because of friction. Friction is an unbalanced force acting on the book to slow it down.

2.2 Types of Forces Static Friction Static friction is the force between two surfaces in contact that keeps them from sliding when a force is applied. A force is applied to a heavy box, but the box doesn’t move. The forces are balanced, the force pushing the box equals the force of static friction pushing in the opposite direction.

2.2 Types of Forces Sliding Friction When the force pushing on the box is larger than the maximum static friction force, the box begins to slide. The frictional force that acts on the sliding box is called sliding friction.

Sliding Friction (cont.) 2.2 Types of Forces Sliding Friction (cont.) The book pushed across the table slows down because of sliding friction. Without sliding friction, the book would continue moving without a force being applied.

Sliding Friction (cont.) 2.2 Types of Forces Sliding Friction (cont.) Usually friction is present and an unbalancing force must be applied to keep an object moving. When friction is greatly reduced, objects move with nearly constant velocity without an applied force.

2.2 Types of Forces Elastic Forces An elastic force occurs when a material is stretched or compressed. A diving board exerts an upward elastic force on the diver when it is bent downward.

2.2 Types of Forces Tension A tension force is a pulling force applied by an object when it is stretched, such as a rubber band.

2.2 Types of Forces Compression A compression force is a squeezing force applied to an object that can make an object shrink. The size of the compression force exerted by a material is equal to the size of the force that compresses the material.

2.2 Types of Forces Normal Forces A normal force is the force exerted by an object that is perpendicular to the surface of the object.

2.2 Types of Forces Normal Forces (cont.) The normal force exerted by the table is an elastic force. The weight of the glass pushing down on the table is a compression force.

2.2 Types of Forces Normal Forces (cont.)

2.2 Types of Forces Normal Forces (cont.)

Forces in the Horizontal Direction 2.2 Types of Forces Forces in the Horizontal Direction Friction balances forces applied in a horizontal direction. Friction equals the horizontal force on an object that is not changing motion.

Forces in the Vertical Direction 2.2 Types of Forces Forces in the Vertical Direction Upward normal force balances the downward force of gravity on an object that is not moving vertically.

Forces in the Vertical Direction (cont.) 2.2 Types of Forces Forces in the Vertical Direction (cont.)

End of Lesson 2