7Contact and Noncontact Sports How do these relate to the title of this lesson? (Gravity and Friction?)Contact = frictionNoncontact = gravity
8Contact ForceA push or pull on one object by another that is touching it.Contact forces can be:StrongORWeak
9Noncontact ForceA force that one object can apply to another object without touching it.Examples Include:GravityMagnetic ForceElectric Force
10Strength and Direction of Forces can be used to show forces.The of an arrow shows theof the force.The that the arrow points shows the direction in which theThe stronger the force the the arrow.ARROWSLENGTHSTRENGTHDIRECTIONFORCE WAS APPLIEDLONGER
11Strength and Direction of Forces The SI unit for force is theThe symbol for Newton isOne Newton = about the force you exert to lift a lime.Named after:NEWTONNSir Isaac Newton (founder of physics)
12Gravity Force of gravity An attractive force that exists between all objects that have mass.Force of gravityOn EARTH the force of gravity = 9.8 m/s2All objects fall to the Earth at an acceleration of 9.8m/s2 due to the force of gravity.
13The Law of Universal Gravitation Sir Isaac Newton (1600’s)The law states:Factors Affecting GravityAll 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.MASSDISTANCE
14MassThe amount of matter in an object.Which object has more mass?
15Gravitational Force and MASS When the mass of one or both objectsthe gravitational force between them alsoRegardless of the amount of mass an object has the will be theEach object exerts the attraction on the other object.INCREASESINCREASESFORCE ARROWSSAME SIZESAME
17Gravitational force and DISTANCE The attraction between objectsas the between the objectDECREASESINCREASESDISTANCE
18Weight The gravitational force exerted on an object. Weight is measured inNear Earth’s surface the object’s weight is theNEWTONSFORCE DUE TO GRAVITY
19Weight and Mass on Earth Weight and mass are related, but ARE NOT the same.Weight can due toMass changeFORCE =CHANGEGRAVITYDOES NOTMASS x ACCELERATIONF =Weight on Earth =M x AMASS x 9.8m/s2 (acceleration due to the force of gravity)
20Examples: What would an object with a mass of 10 kg weigh? If your mass was 50kg, what would your weight be?
21Net 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.
22Combining 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 areForces moving in the opposite direction areADDEDSUBTRACTED
23Combining Forces – Balanced Forces Forces acting on an object that combine and form a net force of ZERO. NO change in motion.
24Friction STATIC FRICTION SLIDING FRICTION FLUID FRICTION A force that resists the motion of two surfaces that are touching.Types of frictionSTATIC FRICTIONSLIDING FRICTIONFLUID FRICTION
25Static FrictionFriction that actson objects thatare not moving.
26Sliding FrictionWhen solid objectsslide over each other.
27Fluid Friction SHAPE SIZE MASS A force produced by a fluid (gases or liquids)Examples: engine oil, greaseAir resistanceAir resistance is affected by:*objects with more surface area have more air resistance**a type of fluid frictionUpward force exerted on falling objects.SHAPESIZEMASS
28What causes friction? 2 causes of friction When microscopic dips and bumps that cover surfaces slide past another surface with dips and bumps they catch on to one another.When a positive charge slides by a negative charge attraction occurs.