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# Force and Motion Review

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8th Grade Force and Motion reveiw.

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### Force and Motion Review

1. 1. Force andMotionReview
2. 2. •A force is simply a push ora pull.•All forces have both sizeand direction.
3. 3. Do you remember…• BrainPop: Force video clip
4. 4. NET FORCESWhen two or moreforces arecombined!
5. 5. Some tips:1. Forces in the same direction- add thetwo forces together.+ =1. Forces in different directions- subtractthe two and figure out which directionwas the stronger of the two.- =
6. 6. Balanced vs. unbalanced forces• Unbalanced: when the net forceon an object is not zero. Theseproduce a change in motion.• Balanced: when the net force onan object equals zero. These doNOT produce change in motion.
7. 7. What is motion?•When an object changesposition over time whencompared with a referencepoint we say that theobject is in motion.
8. 8. Speed• The rate at which an objectmoves.• Depends on distance traveledand the time it takes to travelthat distance.
9. 9. Speed FormulaAverage speed = total distancetotal time
10. 10. Velocity•The speed of an object in aparticular direction***Don’t confuse this withspeed…they don’t meanthe same thing!!
11. 11. • Velocity must ALWAYS includea directionEx: an airplane’s velocity mightbe 600 km/h south
12. 12. •Velocity changes as speedOR direction changes
13. 13. Resultant Velocity.•SAME DIRECTION: add thetwo velocities together.•DIFFERENT DIRECTION:subtract the two velocities.
14. 14. Acceleration•The rate at which velocitychanges.•To change velocity (changespeed or direction or BOTH)• BrainPop: Acceleration video clip
15. 15. • It is not just HOW MUCHvelocity changes, but it is alsoHOW FAST it changes.• The faster velocitychanges, the greater theacceleration is.
16. 16. Acceleration FormulaAcceleration= final velocity – starting velocitytime it takes to change velocity• Velocity is expressed in meters per second (m/s)and time is expressed in seconds (s), so accelerationis expressed in meters per second per second(m/s/s)
17. 17. Newton’s Laws of MotionBrainPop: Newton’s Laws of Motion video clip123
18. 18. Newton’s First Law(law of inertia)An object at rest tends to stay at restand an object in motion tends to stayin motion unless acted upon by anunbalanced force.1
19. 19. Balanced ForceEqual forces in oppositedirections produce no motion
20. 20. Unbalanced ForcesUnequal opposing forcesproduce an unbalanced forcecausing motion
21. 21. Newton’s First Law (law of inertia)• Mass (kg)is the measure of theamount of matter in an object.• INERTIA is a property of an objectthat describes how much it will resistchange to the motion of the object• More mass an object has meansmore inertia the object will have.
22. 22. • There are four main types of friction:–Sliding friction: ex. ice skating–Rolling friction: ex. bowling–Fluid friction (air or liquid): ex. air or waterresistance–Static friction: ex. initial friction whenmoving an objectWhat is this unbalanced force that acts on anobject in motion?
23. 23. This will help up remember:Newton’s First Law video clip
24. 24. Newton’s Second LawForce equals masstimes acceleration.2
25. 25. Newton’s Second LawForce = Mass x Acceleration• Force is measured in Newtons• ACCELERATION of GRAVITY Earth) = 9.8 m/s2• WEIGHT is a measure of the force of gravityon the mass of an object• Weight (force) = mass x gravity (Earth)• BrainPop: Gravity video clip
26. 26. This will help up remember:Newton’s Second Law video clip
27. 27. Newton’s Third LawFor every action there is an equal andopposite reaction.3
28. 28. Newton’s 3rd Law• For every action there is an equal andopposite reaction.Book toearthTable tobook
29. 29. Think about it . . .What happens if you are standing on a skateboard or aslippery floor and push against a wall? You slide in theopposite direction (away from the wall), because youpushed on the wall but the wall pushed back on you withequal and opposite force.Why does it hurt so much when you stub your toe?When your toe exerts a force on a rock, the rock exertsan equal force back on your toe. The harder you hityour toe against it, the more force the rock exerts backon your toe (and the more your toe hurts).
30. 30. Action: earth pulls on youReaction: you pull on earthAction and Reaction on Different MassesConsider you and the earth