Big Idea 13 : Forces And Changes In Motion

Big Idea 13 : Forces and Changes inMotionA. It takes energy to change the motion of objects.B. Energy change is understood in terms of forces--pushes or pulls.C. Some forces act through physical contact while others act at a distance.

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Benchmark Number & Descriptor SC.6.P.13.1 Investigate and describe types of forces including contact forces and forces acting at a distance, such as electrical, magnetic, andgravitational.SC.6.P.13.2Explore the Law of Gravity by recognizing that every object exertsgravitational force on every other object and that the forcedepends on how much mass the objects have and how far apartthey are.SC.6.P.13.3Investigate and describe that an unbalanced force acting on anobject changes its speed, direction of motion, or both.

How did that move?

FORCE A force is apush or a pullon an object. Objects willalways move inthe direction ofthe force.

TYPES OF FORCESBalanced ForceUnbalanced Force Equal forces are applied to Unequal forces are appliedan object. Forces work against eachother and cancel each otherout. Motion or direction doesNOT Change.to an object. Objects motion ordirection will change.

NET FORCE Combination of all forcesacting on an object If the forces are acting inthe same direction on theobject, add the forcestogether. If the forces are acting inthe opposite direction onthe object, subtract theforces.

Knowledge Check 1. What two words describes the term “force”? 2. If two people of the same weight and size sit on oppositesides of a see-saw, what type of force will they represent? If 100 grams of coins are placed on the left side of an equalarm balance and 50 grams were placed on the right side: What type of force will be represented? What will be the net force?

Knowledge Check 1. What two words describes the term “force”?Push and Pull 2. If two people of the same weight and size sit on oppositesides of a see-saw, what type of force will they represent?Balanced force – the see-saw would not move If 100 grams of coins are placed on the left side of an equalarm balance and 50 grams were placed on the right side: What type of force will be represented? Unbalanced force What will be the net force? 50 grams to the left

https://www.youtube.com/watch?v ABMJgz9Ja s

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SLOW IT DOWN!

FRICTIONA force that opposes motionSTATIC FRICTION A force is applied to anobject and no movementoccurs Keeps objects at rest Books are staying in hishand due to static friction.KINETIC FRICTION Friction between movingobjects Three types: Rolling Sliding Air Resistance

EXAMPLES of KINETIC FRICTIONSliding FrictionAir ResistanceRolling Friction

Knowledge Check 1. What is a force which resists motion called? 2. Give an example of static friction. List the three types of kinetic friction and, give an example ofeach.

Knowledge Check 1. What is a force which resists motion called?Friction 2. Give an example of static friction.A box sitting on the floor (no movement) List the three types of kinetic friction and give an example ofeach.Rolling – bike tires in motionSliding – baseball player sliding into the baseAir Resistance – paper airplanes flying through the air

A FORCE TO OVERCOME GRAVITY

GRAVITY Force of attraction between objects due to their masses anddistances apart Universal Force because everything has mass, thereforeeverything is affected by gravity When standing on the Earth, gravity attracts us towards thecenter of the earth so we do not fall off.

Universal Law of Gravitation Isaac Newton concluded that the samelaw of gravity applies to every object inthe universe. The greater the masses of the objects,the larger the gravitational forcebetween them. Finding the gravitationalforce between two objects requiresmultiplying the masses of the twoobjects. If your mass were to be twice asmuch, the gravitational force betweenyou and Earth, which is your weight,would double. If Earth were to becometwice as massive without changing itssize, your weight would also double.Increasing either mass increases thegravitational force between two objects;decreasing their mass decreases /ngravitational force.ewtongrav.htmlRead more at Suite101: Newton's Laws for Kids - Gravity: A Simple Explanation of theLaw of Universal Gravitation newtons laws for kids gravity#ixzz0cvlry8qr

MASS vs. WEIGHT MASSHow much matter, “stuff ”, isin an objectDoes not change whereveryou goStanding on Earth vs.Standing on the Moon youare made of the same “stuff ”,therefore your mass is thesame.Measure mass with a balance WEIGHTCan change at differentlocationsBased on the pull of gravityWeight 100 lbs on EarthWeight 1.6 lbs on themoonGravity is 1/6 of Earthbecause the size of the moonis smaller then the Earth.Measure weight with a springscale

GRAVITY and FALLING OBJECTSACCELERATION All objects fallto the groundwith anacceleration rateof 9.8 m/s2 without thepresence of airresistance.Suppose that an elephant anda feather are dropped off avery tall building from thesame height at the same time.Suppose also that airresistance could somehow beeliminated such that neitherthe elephant nor the featherwould experience any air dragduring the course of their fall.Which object - the elephantor the feather - will hit theground first? The animation atthe right accurately depictsthis situation. The motion ofthe elephant and the featherin the absence of air resistanceis shown. Further, theacceleration of each object isrepresented by a /newtlaws/efff.cfm

GRAVITY and FALLING OBJECTSTERMINALVELOCITY Objects reachterminal velocitywhen the amountof air resistance the pull of y.htm

GRAVITY and FALLING OBJECTSPROJECTILEMOTION When objectsare thrown,they curve tothe ground dueto the roundEarth vectors/pap.cfm

Knowledge Check 1. Why is gravity considered a universal force? 2. What is the difference between mass and weight? 3. What is the acceleration rate on Earth due to gravity? 4. When will a sky diver reach terminal velocity in his/herjump?

Knowledge Check 1. Why is gravity considered a universal force?Gravity affects anything with mass, and every object inthe universe follows the law of gravity 2. What is the difference between mass and weight?Mass stays the same wherever you go.Weight will change due to the factor of gravity. 3. What is the acceleration rate on Earth due to gravity?9.8 m/s2 4. When will a sky diver reach terminal velocity in his jump?When the downward force of gravity the upward force ofair resistance

Who Put This AllTogether .Sir Isaac Newton

Newton’s States: An object atrest/motion stays atrest/motion until anunbalanced force acts on it. Motion Aspect: Cannot beshown on Earth due tofriction Rest Inertia: An object’sresistance to change inmotion. Related directly tomass.st1Law Take a look at this websitepage to see an example ofNewton’s 1st Law. Newton/law1.html Greater mass GreaterinertiaThis marble will not move unlessa force applied to it.

Newton’s States: An object willaccelerate in the samedirection of the force. Motion Aspect:Acceleration is affected bythe mass of the object and theforce applied. Larger mass needs greater force toaccelerate. Formula: Force Mass x Acceleration F MA M F/A A F/Mnd2Law Take a look at this websitepage to see an example ofNewton’s 2nd Law. Newton/law2.html

Newton’s States: For every actionLaw Take a look at this websitethere is an equal andopposite reaction. Motion Aspect:page to see an example ofNewton’s 3rd Law. Action-Reaction Pairs: rd3 http://teachertech.rice.edAct on different objects withequal force at the same -Reaction Pair:Action: Skater pushes on the wall.Reaction: Wall pushes on skater.

TYPES OF FORCES Balanced Force Unbalanced Force Equal forces are applied to an object. Forces work against each other and cancel each other out. Motion or direction does NOTChange. Unequal forces are applied to an object. Objects motion or direction will change.