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Ch. 5 Motion & Forces <ul><li>II. Describing Motion </li></ul><ul><ul><ul><ul><li>Using Newton’s Laws of Motion </li></ul>...
A. Motion <ul><li>Problem: </li></ul><ul><ul><li>Is your desk moving? </li></ul></ul><ul><li>We need a  reference point .....
A. Motion <ul><li>Motion </li></ul><ul><ul><li>Change in position in relation to a reference point. </li></ul></ul>Referen...
A. Motion <ul><li>Problem: </li></ul><ul><li>You are a passenger in a car stopped at a stop sign.  Out of the corner of yo...
A. Force <ul><li>Force </li></ul><ul><ul><li>a push or pull that one body exerts on another </li></ul></ul><ul><ul><li>Wha...
A. Force <ul><li>Balanced Forces </li></ul><ul><ul><li>forces acting on an object that are opposite in direction and equal...
A. Force <ul><li>Net Force </li></ul><ul><ul><li>unbalanced forces that are not opposite and equal </li></ul></ul><ul><ul>...
B. Gravity <ul><li>Gravity   </li></ul><ul><ul><li>force of attraction between any two objects in the universe </li></ul><...
B. Gravity <ul><li>Who experiences more gravity - the astronaut or the politician? </li></ul><ul><li>Which exerts more gra...
B. Gravity <ul><li>Weight </li></ul><ul><ul><li>the force of gravity on an object </li></ul></ul>MASS always the same (kg)...
B. Gravity <ul><li>Would you weigh more on Earth or Jupiter? </li></ul><ul><ul><ul><li>greater gravity </li></ul></ul></ul...
B. Gravity <ul><li>Accel. due to gravity  (g) </li></ul><ul><ul><li>In the absence of air resistance,  all  falling object...
Newton’s First Law <ul><li>Newton’s First Law of Motion </li></ul><ul><ul><li>An object at rest will remain at rest and an...
B. Newton’s First Law <ul><li>Newton’s First Law of Motion </li></ul><ul><ul><li>“ Law of Inertia” </li></ul></ul><ul><li>...
ConcepTest 2 <ul><li>You are a passenger in a car and not wearing your seat belt.  </li></ul><ul><li>Without increasing or...
ConcepTest 2 <ul><li>1. Before and after the collision, there is a rightward force pushing you into the door.  </li></ul><...
What is a Force? <ul><li>Push or pull </li></ul><ul><li>Measured in (N) Newton </li></ul>
Net forces <ul><li>Net force:  all forces exerted on an object </li></ul>
Unbalanced and Balanced Forces <ul><li>Unbalanced forces produce a change in motion(acceleration) </li></ul><ul><li>Balanc...
C. Friction <ul><li>Friction </li></ul><ul><ul><li>force that opposes motion between 2 surfaces </li></ul></ul><ul><ul><li...
C. Friction <ul><li>Friction is greater... </li></ul><ul><ul><li>between rough surfaces </li></ul></ul><ul><ul><li>when th...
Types of Friction <ul><li>Sliding Friction </li></ul><ul><li>Rolling Friction </li></ul><ul><li>Fluid Friction </li></ul><...
Newton’s Second Law <ul><li>Newton’s Second Law of Motion </li></ul><ul><ul><li>The acceleration of an object is directly ...
B. Speed & Velocity <ul><li>Speed </li></ul><ul><ul><li>rate of motion  </li></ul></ul><ul><ul><li>distance traveled per u...
B. Speed & Velocity <ul><li>Instantaneous Speed </li></ul><ul><ul><li>speed at a given instant </li></ul></ul><ul><li>Aver...
B. Speed & Velocity <ul><li>Problem: </li></ul><ul><ul><li>A storm is 10 km away and is moving at a speed of 60 km/h.  Sho...
B. Speed & Velocity <ul><li>Velocity </li></ul><ul><ul><li>speed in a given direction </li></ul></ul><ul><ul><li>can chang...
C. Acceleration <ul><li>Acceleration </li></ul><ul><ul><li>the rate of change of velocity </li></ul></ul><ul><ul><li>chang...
D. Calculations <ul><li>Your neighbor skates at a speed of 4 m/s.  You can skate 100 m in 20 s.  Who skates faster? </li><...
D. Calculations <ul><li>A roller coaster starts down a hill at 10 m/s.  Three seconds later, its speed is 32 m/s.  What is...
D. Calculations <ul><li>Sound travels 330 m/s.  If a lightning bolt strikes the ground 1 km away from you, how long will i...
D. Calculations <ul><li>How long will it take a car traveling 30 m/s  to come to a stop if its acceleration is  -3 m/s 2 ?...
D. Calculations <ul><li>What force would be required to accelerate a 40 kg mass by 4 m/s 2 ? </li></ul>GIVEN: F = ? m = 40...
D. Calculations <ul><li>A 4.0 kg shotput is thrown with 30 N of force.  What is its acceleration? </li></ul>GIVEN: m = 4.0...
D. Calculations <ul><li>Ms. Wills weighs 557 N.  What is her mass?  </li></ul>GIVEN: F(W) = 557 N m = ? a( g ) = 9.8 m/s 2...
ConcepTest <ul><li>Is the following statement true or false? </li></ul><ul><ul><li>An astronaut has less mass on the moon ...
A. Newton’s Third Law <ul><li>Newton’s Third Law of Motion </li></ul><ul><ul><li>When one object exerts a force on a secon...
A. Newton’s Third Law <ul><li>Problem: </li></ul><ul><ul><li>How can a horse  pull a cart if the cart  is pulling back on ...
A. Newton’s Third Law <ul><ul><li>forces are equal and opposite but act on  different  objects </li></ul></ul><ul><ul><li>...
A. Newton’s Third Law <ul><li>Action-Reaction Pairs </li></ul><ul><li>The hammer exerts a force on the nail to the right. ...
A. Newton’s Third Law <ul><li>Action-Reaction Pairs </li></ul><ul><li>The rocket exerts a downward force on the exhaust ga...
A. Newton’s Third Law <ul><li>Action-Reaction Pairs </li></ul><ul><li>Both objects accelerate. </li></ul><ul><li>The amoun...
E. Graphing Motion <ul><li>slope = </li></ul><ul><li>steeper slope = </li></ul><ul><li>straight line = </li></ul><ul><li>f...
E. Graphing Motion <ul><li>Who started out faster? </li></ul><ul><ul><li>A (steeper slope) </li></ul></ul><ul><li>Who had ...
E. Graphing Motion <ul><li>Acceleration is indicated by a curve on a Distance-Time graph. </li></ul><ul><li>Changing slope...
E. Graphing Motion <ul><li>slope = </li></ul><ul><li>straight line = </li></ul><ul><li>flat line = </li></ul><ul><li>accel...
E. Graphing Motion <ul><li>Specify the time period when the object was... </li></ul><ul><li>slowing down </li></ul><ul><ul...
B. Momentum <ul><li>Momentum </li></ul><ul><ul><li>quantity of motion </li></ul></ul>p  =  mv p : momentum (kg ·m/s) m : m...
B. Momentum <ul><li>Find the momentum of a bumper car if it has a total mass of 280 kg and a velocity of 3.2 m/s.  </li></...
B. Momentum <ul><li>The momentum of a second bumper car is 675 kg·m/s.  What is its velocity if its total mass is 300 kg? ...
C. Conservation of Momentum <ul><li>Law of Conservation of Momentum </li></ul><ul><ul><li>The total momentum in a group of...
C. Conservation of Momentum <ul><li>A 5-kg cart traveling at 4.2 m/s strikes a stationary 2-kg cart and they connect.  Fin...
C. Conservation of Momentum <ul><li>A 50-kg clown is shot out of a 250-kg cannon at a speed of 20 m/s.  What is the recoil...
C. Conservation of Momentum <ul><li>So…now we can solve for velocity.  </li></ul>GIVEN: p = -1000 kg·m/s m = 250 kg v = ? ...
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  • Transcript of "Long 50slideschapter 5 motion notes [autosaved]"

    1. 1. Ch. 5 Motion & Forces <ul><li>II. Describing Motion </li></ul><ul><ul><ul><ul><li>Using Newton’s Laws of Motion </li></ul></ul></ul></ul>
    2. 2. A. Motion <ul><li>Problem: </li></ul><ul><ul><li>Is your desk moving? </li></ul></ul><ul><li>We need a reference point ... </li></ul><ul><ul><li>nonmoving point from which motion is measured </li></ul></ul>
    3. 3. A. Motion <ul><li>Motion </li></ul><ul><ul><li>Change in position in relation to a reference point. </li></ul></ul>Reference point Motion
    4. 4. A. Motion <ul><li>Problem: </li></ul><ul><li>You are a passenger in a car stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward. </li></ul><ul><li>You have mistakenly set yourself as the reference point. </li></ul>
    5. 5. A. Force <ul><li>Force </li></ul><ul><ul><li>a push or pull that one body exerts on another </li></ul></ul><ul><ul><li>What forces are being exerted on the football? </li></ul></ul>F kick F grav
    6. 6. A. Force <ul><li>Balanced Forces </li></ul><ul><ul><li>forces acting on an object that are opposite in direction and equal in size </li></ul></ul><ul><ul><li>no change in velocity </li></ul></ul>
    7. 7. A. Force <ul><li>Net Force </li></ul><ul><ul><li>unbalanced forces that are not opposite and equal </li></ul></ul><ul><ul><li>velocity changes (object accelerates) </li></ul></ul>F friction W F pull F net N N
    8. 8. B. Gravity <ul><li>Gravity </li></ul><ul><ul><li>force of attraction between any two objects in the universe </li></ul></ul><ul><ul><li>increases as... </li></ul></ul><ul><ul><ul><li>mass increases </li></ul></ul></ul><ul><ul><ul><li>distance decreases </li></ul></ul></ul>
    9. 9. B. Gravity <ul><li>Who experiences more gravity - the astronaut or the politician? </li></ul><ul><li>Which exerts more gravity - the Earth or the moon? </li></ul>less distance more mass
    10. 10. B. Gravity <ul><li>Weight </li></ul><ul><ul><li>the force of gravity on an object </li></ul></ul>MASS always the same (kg) WEIGHT depends on gravity (N) W = mg W : weight (N) m : mass (kg) g : acceleration due to gravity (m/s 2 )
    11. 11. B. Gravity <ul><li>Would you weigh more on Earth or Jupiter? </li></ul><ul><ul><ul><li>greater gravity </li></ul></ul></ul><ul><ul><ul><li>greater weight </li></ul></ul></ul><ul><ul><ul><li>greater mass </li></ul></ul></ul><ul><ul><li>Jupiter because... </li></ul></ul>
    12. 12. B. Gravity <ul><li>Accel. due to gravity (g) </li></ul><ul><ul><li>In the absence of air resistance, all falling objects have the same acceleration! </li></ul></ul><ul><ul><li>On Earth: g = 9.8 m/s 2 </li></ul></ul>Animation from “ Multimedia Physics Studios .” elephant feather
    13. 13. Newton’s First Law <ul><li>Newton’s First Law of Motion </li></ul><ul><ul><li>An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force. </li></ul></ul>motion constant velocity net force
    14. 14. B. Newton’s First Law <ul><li>Newton’s First Law of Motion </li></ul><ul><ul><li>“ Law of Inertia” </li></ul></ul><ul><li>Inertia (Greek word meaning Lazyness) </li></ul><ul><ul><li>tendency of an object to resist any change in its motion </li></ul></ul><ul><ul><li>increases as mass increases </li></ul></ul>
    15. 15. ConcepTest 2 <ul><li>You are a passenger in a car and not wearing your seat belt. </li></ul><ul><li>Without increasing or decreasing its speed, the car makes a sharp left turn, and you find yourself colliding with the right-hand door. </li></ul><ul><li>Which is the correct analysis of the situation? ... </li></ul>
    16. 16. ConcepTest 2 <ul><li>1. Before and after the collision, there is a rightward force pushing you into the door. </li></ul><ul><li>2. Starting at the time of collision, the door exerts a leftward force on you. </li></ul><ul><li>3. both of the above </li></ul><ul><li>4. neither of the above </li></ul>2. Starting at the time of collision, the door exerts a leftward force on you.
    17. 17. What is a Force? <ul><li>Push or pull </li></ul><ul><li>Measured in (N) Newton </li></ul>
    18. 18. Net forces <ul><li>Net force: all forces exerted on an object </li></ul>
    19. 19. Unbalanced and Balanced Forces <ul><li>Unbalanced forces produce a change in motion(acceleration) </li></ul><ul><li>Balanced Forces produce no change in motion </li></ul>
    20. 20. C. Friction <ul><li>Friction </li></ul><ul><ul><li>force that opposes motion between 2 surfaces </li></ul></ul><ul><ul><li>depends on the: </li></ul></ul><ul><ul><ul><li>types of surfaces </li></ul></ul></ul><ul><ul><ul><li>force between the surfaces </li></ul></ul></ul>
    21. 21. C. Friction <ul><li>Friction is greater... </li></ul><ul><ul><li>between rough surfaces </li></ul></ul><ul><ul><li>when there’s a greater force between the surfaces (e.g. more weight) </li></ul></ul><ul><li>Pros and Cons? </li></ul>
    22. 22. Types of Friction <ul><li>Sliding Friction </li></ul><ul><li>Rolling Friction </li></ul><ul><li>Fluid Friction </li></ul><ul><li>Static Friction </li></ul>
    23. 23. Newton’s Second Law <ul><li>Newton’s Second Law of Motion </li></ul><ul><ul><li>The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. </li></ul></ul><ul><li>F = ma </li></ul>
    24. 24. B. Speed & Velocity <ul><li>Speed </li></ul><ul><ul><li>rate of motion </li></ul></ul><ul><ul><li>distance traveled per unit time </li></ul></ul>v d t
    25. 25. B. Speed & Velocity <ul><li>Instantaneous Speed </li></ul><ul><ul><li>speed at a given instant </li></ul></ul><ul><li>Average Speed </li></ul>
    26. 26. B. Speed & Velocity <ul><li>Problem: </li></ul><ul><ul><li>A storm is 10 km away and is moving at a speed of 60 km/h. Should you be worried? </li></ul></ul><ul><ul><li>It depends on the storm’s direction! </li></ul></ul>
    27. 27. B. Speed & Velocity <ul><li>Velocity </li></ul><ul><ul><li>speed in a given direction </li></ul></ul><ul><ul><li>can change even when the speed is constant! </li></ul></ul>
    28. 28. C. Acceleration <ul><li>Acceleration </li></ul><ul><ul><li>the rate of change of velocity </li></ul></ul><ul><ul><li>change in speed or direction </li></ul></ul>a : acceleration v f : final velocity v i : initial velocity t : time a v f - v i t
    29. 29. D. Calculations <ul><li>Your neighbor skates at a speed of 4 m/s. You can skate 100 m in 20 s. Who skates faster? </li></ul>GIVEN: d = 100 m t = 20 s v = ? WORK : v = d ÷ t v = (100 m) ÷ (20 s) v = 5 m/s You skate faster! v d t
    30. 30. D. Calculations <ul><li>A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s. What is the roller coaster’s acceleration? </li></ul>GIVEN: v i = 10 m/s t = 3 s v f = 32 m/s a = ? WORK : a = ( v f - v i ) ÷ t a = (32m/s - 10m/s) ÷ (3s) a = 22 m/s ÷ 3 s a = 7.3 m/s 2 a v f - v i t
    31. 31. D. Calculations <ul><li>Sound travels 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take for you to hear it? </li></ul>GIVEN: v = 330 m/s d = 1km = 1000m t = ? WORK : t = d ÷ v t = (1000 m) ÷ (330 m/s) t = 3.03 s v d t
    32. 32. D. Calculations <ul><li>How long will it take a car traveling 30 m/s to come to a stop if its acceleration is -3 m/s 2 ? </li></ul>GIVEN: t = ? v i = 30 m/s v f = 0 m/s a = -3 m/s 2 WORK : t = ( v f - v i ) ÷ a t = (0m/s-30m/s)÷(-3m/s 2 ) t = -30 m/s ÷ -3m/s 2 t = 10 s a v f - v i t
    33. 33. D. Calculations <ul><li>What force would be required to accelerate a 40 kg mass by 4 m/s 2 ? </li></ul>GIVEN: F = ? m = 40 kg a = 4 m/s 2 WORK : F = ma F = (40 kg)(4 m/s 2 ) F = 160 N m F a
    34. 34. D. Calculations <ul><li>A 4.0 kg shotput is thrown with 30 N of force. What is its acceleration? </li></ul>GIVEN: m = 4.0 kg F = 30 N a = ? WORK : a = F ÷ m a = (30 N) ÷ (4.0 kg) a = 7.5 m/s 2 m F a
    35. 35. D. Calculations <ul><li>Ms. Wills weighs 557 N. What is her mass? </li></ul>GIVEN: F(W) = 557 N m = ? a( g ) = 9.8 m/s 2 WORK : m = F ÷ a m = (557 N) ÷ (9.8 m/s 2 ) m = 56.8 kg m F a
    36. 36. ConcepTest <ul><li>Is the following statement true or false? </li></ul><ul><ul><li>An astronaut has less mass on the moon since the moon exerts a weaker gravitational force. </li></ul></ul><ul><ul><li>False! Mass does not depend on gravity, weight does. The astronaut has less weight on the moon. </li></ul></ul>
    37. 37. A. Newton’s Third Law <ul><li>Newton’s Third Law of Motion </li></ul><ul><ul><li>When one object exerts a force on a second object, the second object exerts an equal but opposite force on the first. </li></ul></ul>
    38. 38. A. Newton’s Third Law <ul><li>Problem: </li></ul><ul><ul><li>How can a horse pull a cart if the cart is pulling back on the horse with an equal but opposite force? </li></ul></ul><ul><ul><li>Aren’t these “balanced forces” resulting in no acceleration? </li></ul></ul>NO!!!
    39. 39. A. Newton’s Third Law <ul><ul><li>forces are equal and opposite but act on different objects </li></ul></ul><ul><ul><li>they are not “balanced forces” </li></ul></ul><ul><ul><li>the movement of the horse depends on the forces acting on the horse </li></ul></ul><ul><li>Explanation: </li></ul>
    40. 40. A. Newton’s Third Law <ul><li>Action-Reaction Pairs </li></ul><ul><li>The hammer exerts a force on the nail to the right. </li></ul><ul><li>The nail exerts an equal but opposite force on the hammer to the left. </li></ul>
    41. 41. A. Newton’s Third Law <ul><li>Action-Reaction Pairs </li></ul><ul><li>The rocket exerts a downward force on the exhaust gases. </li></ul><ul><li>The gases exert an equal but opposite upward force on the rocket. </li></ul>F G F R
    42. 42. A. Newton’s Third Law <ul><li>Action-Reaction Pairs </li></ul><ul><li>Both objects accelerate. </li></ul><ul><li>The amount of acceleration depends on the mass of the object. </li></ul><ul><li>Small mass  more acceleration </li></ul><ul><li>Large mass  less acceleration </li></ul>F m
    43. 43. E. Graphing Motion <ul><li>slope = </li></ul><ul><li>steeper slope = </li></ul><ul><li>straight line = </li></ul><ul><li>flat line = </li></ul>faster speed constant speed no motion speed Distance-Time Graph A B
    44. 44. E. Graphing Motion <ul><li>Who started out faster? </li></ul><ul><ul><li>A (steeper slope) </li></ul></ul><ul><li>Who had a constant speed? </li></ul><ul><ul><li>A </li></ul></ul><ul><li>Describe B from 10-20 min. </li></ul><ul><ul><li>B stopped moving </li></ul></ul><ul><li>Find their average speeds. </li></ul><ul><ul><li>A = (2400m) ÷ (30min) A = 80 m/min </li></ul></ul><ul><ul><li>B = (1200m) ÷ (30min) B = 40 m/min </li></ul></ul>Distance-Time Graph A B
    45. 45. E. Graphing Motion <ul><li>Acceleration is indicated by a curve on a Distance-Time graph. </li></ul><ul><li>Changing slope = changing velocity </li></ul>Distance-Time Graph
    46. 46. E. Graphing Motion <ul><li>slope = </li></ul><ul><li>straight line = </li></ul><ul><li>flat line = </li></ul><ul><li>acceleration </li></ul><ul><ul><li>+ve = speeds up </li></ul></ul><ul><ul><li>-ve = slows down </li></ul></ul>constant accel. no accel. (constant velocity) Speed-Time Graph
    47. 47. E. Graphing Motion <ul><li>Specify the time period when the object was... </li></ul><ul><li>slowing down </li></ul><ul><ul><li>5 to 10 seconds </li></ul></ul><ul><li>speeding up </li></ul><ul><ul><li>0 to 3 seconds </li></ul></ul><ul><li>moving at a constant speed </li></ul><ul><ul><li>3 to 5 seconds </li></ul></ul><ul><li>not moving </li></ul><ul><ul><li>0 & 10 seconds </li></ul></ul>Speed-Time Graph
    48. 48. B. Momentum <ul><li>Momentum </li></ul><ul><ul><li>quantity of motion </li></ul></ul>p = mv p : momentum (kg ·m/s) m : mass (kg) v : velocity (m/s) m p v
    49. 49. B. Momentum <ul><li>Find the momentum of a bumper car if it has a total mass of 280 kg and a velocity of 3.2 m/s. </li></ul>GIVEN: p = ? m = 280 kg v = 3.2 m/s WORK : p = mv p = (280 kg)(3.2 m/s) p = 896 kg·m/s m p v
    50. 50. B. Momentum <ul><li>The momentum of a second bumper car is 675 kg·m/s. What is its velocity if its total mass is 300 kg? </li></ul>GIVEN: p = 675 kg·m/s m = 300 kg v = ? WORK : v = p ÷ m v = (675 kg·m/s)÷(300 kg) v = 2.25 m/s m p v
    51. 51. C. Conservation of Momentum <ul><li>Law of Conservation of Momentum </li></ul><ul><ul><li>The total momentum in a group of objects doesn’t change unless outside forces act on the objects. </li></ul></ul>p before = p after
    52. 52. C. Conservation of Momentum <ul><li>A 5-kg cart traveling at 4.2 m/s strikes a stationary 2-kg cart and they connect. Find their speed after the collision. </li></ul>BEFORE Cart 1 : m = 5 kg v = 4.2 m/s Cart 2 : m = 2 kg v = 0 m/s AFTER Cart 1 + 2 : m = 7 kg v = ? p = 21 kg·m/s p = 0 p before = 21 kg·m/s p after = 21 kg·m/s v = p ÷ m v = (21 kg·m/s) ÷ (7 kg) v = 3 m/s m p v
    53. 53. C. Conservation of Momentum <ul><li>A 50-kg clown is shot out of a 250-kg cannon at a speed of 20 m/s. What is the recoil speed of the cannon? </li></ul>BEFORE Clown : m = 50 kg v = 0 m/s Cannon : m = 250 kg v = 0 m/s AFTER Clown : m = 50 kg v = 20 m/s Cannon : m = 250 kg v = ? m/s p = 0 p = 0 p before = 0 p = 1000 kg·m/s p after = 0 p = -1000 kg·m/s
    54. 54. C. Conservation of Momentum <ul><li>So…now we can solve for velocity. </li></ul>GIVEN: p = -1000 kg·m/s m = 250 kg v = ? WORK : v = p ÷ m v = (-1000 kg·m/s)÷(250 kg) v = - 4 m/s (4 m/s backwards) m p v
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