The Laws of Motion Essential Question How do

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

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

Part 1: Forces

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

Types of Force � Contact Force � Non-Contact Force

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

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

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

Part 2: Friction

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

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

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 � An attractive force that exists between all objects that have mass. Force of gravity � On � All EARTH the force of gravity = 9. 8 m/s 2 objects fall to the Earth at an acceleration of 9. 8 m/s 2 due to the force of gravity.

The Law of Universal Gravitation � Sir Isaac Newton (1600’s) � The law states: �Factors 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. Affecting Gravity • MASS • DISTANCE

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

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

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

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

Weight and Mass on Earth � Weight and mass are related, but ARE NOT the � Weight can same. � Mass CHANGE due to GRAVITY DOES NOT change FORCE = MASS x ACCELERATION F= Mx. A Weight on Earth = MASS x 9. 8 m/s 2 (acceleration du to the force of gravity)

Examples: � What would an object with a mass of 10 kg weigh on Earth? � If your mass was 50 kg, 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 ADDED � Forces moving in the opposite direction are 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.