The Laws of Motion Essential Question: How do forces change to motion of an object? Original ppt from Mrs. West’s 8th Grade Physics WEbsite http://kawameeh.twpunionschools.org/subsites/hbormann/index.html Adapted by Denise Poston 2015

True or False. What do you think True or False? What do you think? Only some of the statements below are true. Can you identify them?

Part 1: Forces

Force STRENGTH DIRECTION STOP MOVING START MOVING CHANGE DIRECTION A push or pull on an object. Described by: A force gives an object energy to: STRENGTH DIRECTION STOP MOVING START MOVING CHANGE DIRECTION

Types of Force Contact Force Non-Contact Force

Types of Force Contact Force Noncontact Force Contact forces can be: A force that one object can apply to another object without touching it. A push or pull on one object by another that is touching it. Contact forces can be: Strong OR Weak Examples Include: Gravity Magnetic Force Electric Force

Strength and Direction of Forces can be used to show forces. The of an arrow shows the of the force. The that the arrow points shows the direction in which the The stronger the force the the arrow. ARROWS LENGTH STRENGTH DIRECTION FORCE WAS APPLIED LONGER

Strength and Direction of Forces The SI unit for force is the The symbol for Newton is One Newton = about the force you exert to lift a lime. Named after: NEWTON N Sir Isaac Newton (founder of physics)

Part 2: Friction

Friction STATIC FRICTION SLIDING FRICTION FLUID FRICTION A force that resists the motion of two surfaces that are touching. Types of friction STATIC FRICTION SLIDING FRICTION FLUID FRICTION

Static Friction Friction that acts on objects that are not moving.

Sliding Friction When solid objects slide over each other.

Fluid Friction SHAPE SIZE MASS A force produced by a fluid (gases or liquids) Examples: engine oil, grease Air resistance Air resistance is affected by: *objects with more surface area have more air resistance* a type of fluid friction Upward force exerted on falling objects. SHAPE SIZE MASS

What causes friction? 2 causes of friction Surface roughness (texture) Attraction between particles (positive and negative)

Have you changed your mind about any of these?

Part 3: Gravity How does the force of gravity change the motion of an object?

Gravity Force of gravity An attractive force that exists between all objects that have mass. Force of gravity On EARTH the force of gravity = 9.8 m/s2 All objects fall to the Earth at an acceleration of 9.8 m/s2 due to the force of gravity.

The Law of Universal Gravitation Sir Isaac Newton (1600’s) The law states: Factors Affecting Gravity All objects are attracted to each other by a gravitational force. The strength of force depends on the MASS of each object and the DISTANCE between them. MASS DISTANCE

Mass Which object has more mass? Which object has more mass? The amount of matter in an object. Which object has more mass? Which object has more mass?

Gravitational Force and MASS When the mass of one or both objects the gravitational force between them also Regardless of the amount of mass an object has the will be the Each object exerts the attraction on the other object. INCREASES INCREASES FORCE ARROWS SAME SIZE SAME

Gravitational force and DISTANCE The attraction between objects as the between the object DECREASES INCREASES DISTANCE

Weight The gravitational force exerted on an object. Weight is measured in Near Earth’s surface the object’s weight is the NEWTONS FORCE DUE TO GRAVITY

Weight and Mass on Earth Weight and mass are related, but ARE NOT the same. Weight can due to Mass change FORCE = CHANGE GRAVITY DOES NOT MASS x ACCELERATION F = Weight on Earth = M x A MASS x 9.8m/s2 (acceleration due to the force of gravity)

Examples: What would an object with a mass of 10 kg weigh on Earth? If your mass was 50kg, what would your weight be on Earth?

Net Force The combination of all the forces acting on an object. To calculate the net force: If the forces act in the same direction they are added together. If forces act in opposite directions they are subtracted.

Combining Forces - Unbalanced Forces acting on an object that combine and form a net force that is not zero. Unbalanced forces cause an object to move. Forces moving in the same direction are Forces moving in the opposite direction are ADDED SUBTRACTED

Combining Forces – Balanced Forces Forces acting on an object that combine and form a net force of ZERO. NO change in motion.

Any last revisions? Rewrite any false statements to make them true.