1. Forces Ch. 12.1

2. TrueFalseStatementTrueFalse Force causes objects at rest to move, or objects moving to keep moving Balanced forces have a net force of zero, so the object doesn’t move. Unbalanced forces have a net force, and cause acceleration The 3 types of friction are rolling, sliding, and fluid (air and liquid) Gravity acts towards the center of the Earth, 9.8 m/s2 Projectile motion allows a ball to be thrown in a straight line

3. Force A push or pull on an object Causes a resting object to move Can change a moving object by changing speed or direction

4. Force Measuring ForceUnits of Force Newton Spring Scales Weight Direction of arrow= direction of force Length of arrow= strength/magnitude Newtons, N Force causing 1 kg mass to accelerate at 1 m/s2 1 N = 1 kg · m/s2 Named after Sir Isaac Newton Representing Force Free Body Diagram Practice

5. Combining Forces net force- overall force acting on an object after all forces are combined Balanced ForcesUnbalanced Forces Net force = zero No change in motion Net force zero Object accelerates

6. Friction Force that opposes motion of objects

7. Types of Friction Static FrictionSliding Friction Force acting on objects that are not moving Acts opposite to applied force Ex: walking Force opposing direction of motion of an object as it slides over a surface Sliding friction < static friction Less force needed to keep moving than to start

8. Types of Friction Rolling FrictionFluid Friction/Air resistance Force that acts on rolling objects 100-1000 < Static or rolling friction Ex: ball bearings, wheels Opposes motion of objects through fluid Friction increases as speed increases

9. Gravity Force that acts between 2 masses *force of gravity doesn’t require objects to be in contact Earths gravity acts downward toward center of Earth ______ Falling Objects ▫ Gravity=accelerate downward ▫ Air resistance= opposite motion/reduce acceleration ▫ Terminal Velocity- constant velocity of falling objects. Air resistance = force of gravity

10. Projectile Motion Motion of a falling object, after given an initial forward velocity Air resistance and gravity = only forces Forward force velocity, and downward vertical gravity = curved path

11. Newton’s 1 st and 2 nd Laws of Motion Ch 12.2

12. TrueFalseStatementTrueFalse Aristotle, Galileo, and Newton helped discover forces, and laws of motion Newtons 1 st law, states an object and rest stays at rest, and an object in motion stays in motion Newtons 2 nd law is Force= mass x acceleration Newtons 1 st law can also be called the law of inertia Weight = mass x gravity Mass and weight are the same

13. History of Motion Aristotle 384bc-322bc ▫ Force is required to keep an object moving at constant speed WRONG!! Galileo 1564-1642 ▫ Gravity yields constant acceleration ▫ Objects without friction/force would move indefinitely Newton 1665 ▫ Defined mass and force ▫ 3 Laws of Motion

14. Newton’s 1 st Law of Motion The state of motion of on object does not change as long as the net force acting on the object is zero Unless unbalanced forces act: ▫ An object at rest, stays at rest ▫ An object moving, remains at motion in the same direction and speed

15. Newton’s 1 st Law of Motion Also called Law of Inertia ▫ Tendency of an object to resist a change in motion

16. Newton’s 2 nd Law of Motion The acceleration of an object is equal to the net force acting on it divided by the objects mass Mass- the measure of the inertia of an object. Depends on the amount of matter in the object

17. Newton’s 2 nd Law of Motion F= ma F= m= a= SI Units ▫ a= N/Kg = m/s2 ▫ F = N ▫ m= kg or m

18. Practice A car with a mass of 1000Kg accelerates when the light turns green. If the net force on the car is 4000 N, what is the cars acceleration? Given info ▫ m= ▫ F= ▫ a= Formula Plug and chug Check

19. Math Practice pg 367 1. 2. 3. 4.

20. Weight and Mass Weight- force of gravity acting on an object. Product of the objects mass and acceleration due to gravity Weight = Mass x Acceleration due to gravity W = mg

21. Practice If an astronaut has a mass of 112kg, what is his weight on Earth where acceleration due to gravity is 9.8m/s2? Given ▫ W= ▫ m= ▫ g= Equation Plug and Chug Check

22. Mass = 88kg Weight= 863NWeight = 141N

23. Newton’s 3 rd Law of Motion Ch 12.3

24. TrueFalseStatementTrueFalse Momentum is mass x velocity, or P = m x v Newtons 3 rd law says that when objects exert force on each other, it is equal and opposite Action and reaction forces do not always have to be paired A roller coaster at rest has less momentum than a rolling bowling ball Momentum is conserved in open and closed systems

25. Newton’s 3 rd Law Whenever one object exerts force on a second object, the second exerts an equal and opposite force on the first object Action and reaction forces

26. Action and Reaction Forces Equal in size, opposite in direction Pushing against a wall ▫ Hand force = action ▫ Wall force = reaction

27. Action and Reaction Forces MotionDo not cancel Swimming- Motion ▫ Arms = action, push water ▫ Water = reaction, push person Not all create motion Net force is not zero ▫ Action-reaction forces do not act on the same object Net force is zero ▫ Action-reaction forces act on same object

28. Momentum The product of an objects mass and velocity

29. Calculating Momentum SI units ▫ Kg · m/s Which has more momentum: a 0.0460m kg golf ball at 60 m/s or a 7 kg bowling ball at a speed of 6 m/s? Given: Formula: Plug and chug:

30. Conservation of Momentum Momentum does not increase or decrease If no net force acts on a system(closed system), momentum does not change

31. Universal Forces Ch 12.4

32. TrueFalseStatementTrueFalse Electromagnetic forces are electrons and magnets Both weak and strong nuclear forces are powerful The law of universal gravitation states that every object in the universe attracts every other object Gravity is the strongest universal force, holding us to earth, and keeping the moon in orbit Electromagnetic forces are the only force to attract and repel

33. Electromagnetic Forces Associated with charged particles Electric forces and magnetic forces are the only forces that attract and repel

34. Electromagnetic Forces Electric ForcesMagnetic Forces Between charged particles ▫ Electron and protons Opposite charges ▫ Attract Same ▫ repel 2 poles ▫ North and South Opposite ▫ Attract Same ▫ repel

35. Nuclear Forces 2 forces Strong nuclear and weak nuclear force at to hold the nucleus together

36. Nuclear Forces StrongWeak Powerful force Acts only on neutrons and protons – holding them together Can work over long distances Powerful force Weaker than strong force Holds together in short distances

37. Gravitational Forces Attractive force between any 2 masses Newton’s Law of Gravitation ▫ Every object in the universe attracts every other object ▫ Ex- earth exerts force on apple, apple exerts force on earth

38. Gravitational Forces Gravity Acts over large DistancesEarth, Moon, Tides Force is proportional to mass and decreases as the distances increases Gravity- weakest universal force, but effective over large distances Earths gravitational attraction keeps moon circling around Earth Centripetal force- ▫ Center directed force that continually changes the direction of an object to make it move in a circle Tides- pull of moon ▫ High tide ▫ Low tide