Forces and Motion Forces and Motion? Newton’s Laws of Motion? Mechanical Advantage and Simple Machines?

FORCES AND MOTION LEQ: How do forces cause a change in motion and how is it a result of potential and kinetic energy?

Vocabulary Preview- Activating Word splash Force Gravity Air Resistance Unbalanced force Balanced force Friction Speed Velocity Potential Energy Acceleration Kinetic Energy

What is a Force? In science, a force is a push or a pull. All forces have two properties: Direction and Size A newton (N) is the unit that describes the size of a force.

What is a Force? The student is pushing down on the chair, but the chair does not move. The floor is balancing the force by pushing on the chair.

How do Forces Combine? More than one force often acts on an object. When all the forces acting on an object are added together, you determine the net force on the object. An object with a net force more than 0 N on it will change its state of motion.

Forces in the Same Direction When forces are applied in the same direction, they are added to determine the size of the net force.

Forces in Different Directions When two forces act in opposite directions, you subtract the smaller force from the larger force to determine the net force. The net force will be in the same direction as the larger force.

Balanced and Unbalanced Forces When the forces on an object produce a net force of 0 N, the forces are balanced. There is no change in the motion of the object.

Balanced and Unbalanced Forces When the net force on an object is not 0 N, the forces on the object are unbalanced. Unbalanced forces produce a change in motion of an object.

Balanced and Unbalanced Forces

What is gravity? Galileo first to test gravity with Law of Falling Bodies Sir Isaac Newton concluded that a force acts to pull objects straight down toward the center of the Earth. Gravity is a force that pulls objects toward each other.

How are Weight and Mass related? Mass is the measure of the amount of matter in an object Weight is a measure of the gravitational force exerted on an object Weight varies with the strength of the gravitational force, but mass does not Mass weight gizmo

What are the Factors Affecting Gravity? Mass – more mass an object has, the greater its gravitational force Distance – the farther apart two objects are, the less gravitational force between them

How is Earth affected by gravity? The sun’s mass is so great that it exerts a large gravitational force on the planets – One reason why they stay in orbit. The Moon is constantly falling toward Earth and would continue to move in a straight line and would not orbit Earth. The same is true of the planets and their moons, stars, and all orbiting bodies throughout the universe.

Earth – Moon – Sun Relationship

How does Air Resistance Affect Gravity? Falling objects with a greater surface area experience more air resistance, which is a fluid friction caused by air molecules against a surface or area. In a vacuum there is no air, all objects fall at the same rate of acceleration

Factors affecting air resistance speed of the object -Increased speeds result in an increased amount of air resistance. surface area of the object- Increased surface areas areas result in an increased amount of air resistance. Ex. Parachute

What Causes Friction? Friction is the force that opposes the motion between two surfaces that touch. The surface of any object is rough. Even an object that feels smooth is covered with tiny hills and valleys, resulting in friction.

The amount of friction depends on: What Causes Friction? The amount of friction depends on: Roughness of the surfaces Force pushing the surfaces together

Types of Friction Kinetic friction occurs when force is applied to an object and the object moves. Examples: Sliding Friction: pushing an object across a surface Rolling Friction: between wheels and a surface Fluid Friction: opposes the motion of objects traveling through a fluid (air or water)

Types of Friction Static friction occurs when force applied to an object does not cause the object to move.

Affecting Friction To reduce the amount of friction, apply a lubricant between two surfaces. Motor oil, wax, and grease are examples. Friction can also be reduced by rolling, rather than pushing, an object.

Affecting Friction Friction increases as surfaces are made rougher. Friction increases when the force between two objects is increased.

Inertia The tendency of an object to resist changes in its state of motion varies with mass. Mass is that quantity that is solely dependent upon the inertia of an object. The more inertia that an object has, the more mass that it has. A more massive object has a greater tendency to resist changes in its state of motion.