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# Motion Notes 2005

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### Transcript

• 1. MECHANICS
• 2. Motion Chapter 1 Notes
• 3. What is a RATE?
• A rate tells how fast something happens.
• Some rates that we will use to describe motion are:
• Speed
• Velocity
• Acceleration
• 4. What is Motion???
• A change in position.
• 5. What is speed?
• Rate of Change in Position.
• “Rate of Motion”
• Types of Speed
• Instantaneous
• Constant
• Average
• 6. Speed Formula
• speed = the change in distance
• the change in time
• v = ∆ d
• ∆ t
• ∆ is the Greek letter DELTA. In science this means CHANGE.
• 7. Speed Units
• m/s
• km/s
• m/h
• km/h
• When you read the first unit, you say meters “PER” second.
• Do not write mps
• 8. Instantaneous Speed
• The rate of motion at a given instant.
• A speedometer in a car shows the instantaneous speed of the car.
• 9. Average Speed
• On a trip from Chicago to Texas could you stay the same speed?
• You could get an average of all the speeds during the trip.
• 10.
• 11. How do we calculate average speed?
• The total distance of the trip divided by the total time of travel.
• 12. Constant Speed
• A speed that does not change over a period of time.
• Cruise Control in a car.
• 13. Any questions about the Section Review Questions?
• Page 14
• 14. Speed is Relative!
• What does it mean when we say that a car moves at a rate of 80 km/h?
• What do we mean that it is relative to?
• Unless the problem says something else, the motion that we discuss is ALWAYS relative to Earth.
• 15. Everything is in constant motion
• Do you agree?
• 16. Galileo
• Why did he have such difficulty spreading his findings?
• 17. Velocity Notes 1.2
• 18. What is Velocity?
• Describes the motion and the direction .
• Even if speed remains the same, if the direction changes then the velocity has changed.
• 19. Any questions about the Section Review Questions?
• Page 16
• 20. VELOCITY VECTORS
• VECTOR: An arrow drawn to scale that represents the magnitude and direction of a given velocity.
10m/s left 5m/s rt
• 21.
• RESULTANT: The single vector that results when two vectors are combined.
10m/s left 5m/s rt 5m/s left
• 22. Turn to the question on Page 17:
• A motor boat is moving 10 km/h relative to the water. If the boat travels in a river that flows at 10km/h, what is the velocity relative to the shore when it heads directly up stream?
• When it heads directly downstream?
• 23. Now, let’s Check Your Understanding!
• 24. Calculating Average Speed / Velocity
• d= distance
• v= speed / velocity
• t= time
• 25. Follow the steps to solve an equation.
• Problem: You walk 5 meters in 3 seconds. What is your velocity?
• Step 1: Write what you know.
• d = 5 meters
• t = 3 seconds
• v = ?
• Step 2: Write the formula you will use. v = d / t
• Step 3: Put the numbers in for the variables that you know.
• v = 5 meters
• 3 seconds
• Step 4: Do the math.
• v = 1.6667meters/seconds = 1.7m/s
• Your velocity is 1.7 meters per second.
• 26. Equations for Speed and Velocity
• v = d / t
• d = v  t
• t = d / v
• 27. Sample Speed / Velocity Problems
• A car travels a distance of 16 m in 1.8 seconds. What is it’s speed?
• d = 16 m
• t = 1.8 s
• v = ?
• v = d/t
• v = 16m / 1.8s
• v = 8.89 m/s
• 28. Sample Speed / Velocity Problems
• Sound travels at a speed of 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take for the sound to reach you?
• v = 330m/s
• d = 1km
• t = ?
• t = d/v
• t = 1km / 330m/s
• t = 1000m / 330m/s
• t = 3.03 s
• Complete the worksheet.
• 30. Acceleration Section 1.3
• 31. What is Acceleration?
• The rate of change of velocity.
• Car commercial  0 to 60 mph in 10 seconds.
• Speeding up
• The amount of change of velocity in a time interval.
• 32.
• 33. How do you measure a change?
• The water was at 50m and it rose to 100m. What is the change?
• We started at 9:00am and the class was over at 11:00am. What is the change?
• The dog grew from 8 lbs to 15 lbs. What is the change?
• We had 20 gallons, and now we have 5. What is the change?
• 34. How to Calculate Acceleration?  means “change in”
• 35. How do you calculate Δv?
• The change in velocity = the final velocity – the initial velocity.
• Δv = v f – v i
• You are stopped at a red light. When it turns green, you speed up to 45m/s. What is your change in velocity?
• v i = 0m/s
• v f = 45m/s
• Δv = ?
• Δv = v f -v i = 45m/s- 0m/s = 45m/s
• 36. Acceleration Units
• velocity unit/ time unit
• km/h/s
• m/s/s
• or m/s 2
• 37. What are some other ways to say that the car is accelerating?
• 38. Any questions about the Section Review Questions?
• Page 20
• 39. What is negative acceleration?
• Also known as DECELERATION.
• The negative rate of change of velocity.
• Slowing down.
• The amount of negative change of velocity in a time interval.
• 40. How does it feel?
• When you accelerate?
• When you decelerate?
• 41. Look at Fig 1.10 on pg 21
• Which ball will hit the ground first?
• Which ball accelerates the most?
• Which ball will have the fastest speed at the end?
A B C D
• 42. What did Galileo find from the ramp experiment?
• Steeper inclines = greater acceleration
• All materials fall with the same acceleration. (when you can neglect air resistance)
• 43. How will we use the acceleration formula to solve problems?
• a =  v /  t
•  v = a X  t
•  t =  v / a
• 44.
• 45. Let’s Practice with some Problems
• A car’s velocity changes from 0 m/s to 30 m/s in 10 seconds. Calculate the car’s average acceleration.
•  v = 30m/s
•  t = 10s
• a = ?
• a =  v /  t
• a = 30 m/s / 10s
• a = 3 m/s/s or 3 m/s 2
• 46. Practice Problems
• A swimmer speeds up from 1.1 m/s to 1.3 m/s during the last 20 s of the workout. What is the acceleration during this interval?
•  v = 1.3 m/s – 1.1 m/s = 0.2m/s
•  t = 20s
• a = ?
• a =  v /  t
• a = 0.2 m/s / 20s
• a = 0.01 m/s/s or m/s 2
• 47. Let’s Review Speed!
• http://www.unitedstreaming.com/
• 48. Graphing Motion Review
• 49.
• 50.
• 51.
• 52.
• 53.
• 54. FREE FALL
• A falling object that has only the force of gravity working on it.
• 55. What pattern do you notice? Table 1.2 (pg. 22) 10 t t * * 50 5 40 4 30 3 20 2 10 1 0 0 Instantaneous Speed (m/s) Time of free fall (s)
• 56. What is the acceleration of any free falling object ?
• The table shows that the velocity increases 10 meters per second for each second that it falls.
• So a = 10 m/s/s or 10 m/s 2
• 57. g
• g = ACCELERATION DUE TO GRAVITY
• g = - 9.8 m/s/s
• If you are calculating, use -9.8m/s/s
• Why do we use negative numbers when we describe an object falling?
• 58. Let’s review the acceleration formulas! a v t
• 59. The formulas you will use:
• a = Δ v / Δ t
• Δ v = a X Δ t
• Δ t = Δ v / a
• REMEMBER:
• Δv = final v – initial v
• Δt = final t – initial t
• 60. A NEW FORMULA
• distance = ½ (acceleration X time X time)
• d = ½ (at 2 )
• Your book says d = ½ (gt 2 ) when talking about falling objects…why?
• 61. Does our formula work? ½ 10 t 2 t * * 125 5 80 4 45 3 20 2 5 1 0 0 Distance of fall (m) Time of free fall (s)
• 62. Feather & Hammer drop
• Which would hit the ground first?
• Why?
• 63. Let’s Practice!
• Let’s try the example!
• 64. What is the velocity of a rubber ball dropped from a building roof after 5 seconds?
• v f = ?
• v i = 0 m/s
• t = 5 s
• a = -9.8 m/s 2
• Δv = a X Δ t
• Δ v = -9.8 m/s 2 X 5 s
• Δ v = -49 m/s
• Δ v = v f –v i
• -49m/s = v f – 0 m/s
• v f = -49 m/s or 49 m/s down
• 65. HOMEWORK
• Worksheets 20 & 21
• Complete ALL problems.
• 66. Let’s review falling objects & Check out Galileo’s experiments!
• http://www.unitedstreaming.com/
• 67. Newton’s Laws
• Which law is shown here?
• How do you know?
• 68.
• 69.
• 70.
• 71.
• 72.
• 73.
• 74.
• 75.
• 76.
• 77. DINNER PARTY EXAMPLE…
• 78. Forces Notes 3.4
• 79. What is a Force?
• A push or pull on an object.
• Some forces are seen, for example a box being pushed across the table.
• Some forces are not seen, for example the floor pushing up on your feet.
• 80.
• 81. Balanced Forces
• A balanced force is a force on an object that is equal in size and opposite in direction.
• Tug of war is a good example.
• Each person is pulling on the other with an equal and balanced force.
• 82.
• 83.
• 84. Unbalanced Forces
• Sometimes forces are not equal or opposite.
• Example: Pushing a car.
• An unbalanced force is a net force.
• A net force acting on an object will change the velocity and/or direction .
• 85.
• 86. Why do objects stand still if no force is applied?
• Inertia!
• The tendency of objects to resist a change in motion.
• If it is moving – it will keep moving.
• If it is still – it will not move.
• UNLESS….. A net force acts on it!
• 87. Inertia
• Examples:
• A book on your desk will sit there and not move, unless you apply a force to the book to move it. If your arm pushed the book, that would be a force.
• If you drive in a car and hit a wall without the force of a seat belt to stop you, your body will continue to move even though the car has stopped. This is why people go through the windshield.
• 88.
• 89. Which object has more inertia?
• Heavier objects are harder to stop moving and start moving.
• The larger the mass, the greater the inertia.
• Example: A semi truck is harder to stop than a toy truck.
• 90. Newton’s First Law of Motion (Law of Inertia)
• “An object moving at a constant velocity will keep moving at that velocity unless a net force acts on it. If an object is at rest it will stay at rest unless a net force acts on it.”
• An object in motion will stay in motion (rest at rest)
• Hmmm- Isn’t that Inertia?
• 91. Why don’t object stay moving forever????
• If the Law of Inertia is true, than any moving object should move forever!
• In outer space this is true because there is no friction.
• 92. What is Friction?
• The force that pushes in the opposite direction of motion between two surfaces that are touching each other.
• For Example: A car will eventually slow down because of the friction between the car tires and the road.
• 93.
• 94. Gravity Notes 3.5
• 95. What is Gravity?
• The force in the universe between all objects.
• Every object in the universe exerts a force on other objects.
• 96. Gravitational Force
• The amount of force that gravity exerts is called gravitational force.
• How much gravitational force there is depends on the mass and distance between objects
• 97. Gravitational Forces Example
• Earth is larger than the moon, therefore the moon is stuck in the gravitational pull of the earth.
• 98. Gravity and Weight
• The measure of the force of gravity on an object is weight.
• Weight is different from mass!!!
• 99. Mass vs. Weight Scale Balance Measuring Tool Changed by location Newton (N) Amount of gravitational force acting on an object Weight Not changed by location g, kg The amount of matter in an object Mass Location Unit Definition
• 100. Mass vs. Weight
• Mass is not a force. It is a quantity.
• Weight is the force of gravity on an object.
• A mass of 1 kg weighs 9.8 N.
• 101. Newton’s Second Law Notes 4.1
• 102. Newton’s Second Law of Motion
• This Law is best explained as an equation.
• Force = mass x acceleration
• The net force acting on an object causes that object to accelerate in the direction of the force.
• 103. Newton’s Second Law of Motion Example:
• How much force is needed to accelerate a 70 kg rider and her 200 kg motorcycle at 4 m/s 2 ?
• F = m x a
• F = 270kg x 4 m/s 2
• F = 1080 kg  m / s 2 or N
• 104. What is a Newton?
• F = m x a
• F = kg x m/s 2
• F = kg m
• s 2
• 1 kg m = 1 Newton
• s 2
• 105. How do I calculate weight?
• Because any force can be calculated using the equation F = m x a , weight of an object (a force) can be calculated using a similar equation W = m x a .
• Because weight is the force of gravity on an object the rate of acceleration is the pull of gravity. (remember? 9.8 m/s 2 )
• 106. Weight Example
• W = m x g (g = gravity)
• If a person has a mass of 50 kg what is their weight?
• W = m x g
• W = 50 kg x 9.8 m/s 2
• W = 490 N
• 107. Acceleration Caused by the Force of Gravity
• Gravity is a force that pulls objects towards the center of an object. (Earth)
• Near the Earth’s surface, gravity causes all falling objects to accelerate at 9.8 m/s 2 .
• Acceleration due to gravity is the same for all objects.
• 108. The bowling ball and the feather…
• If acceleration due to gravity is the same for all objects, regardless of mass, then all objects should fall at the same rate.
• Does a leaf fall as fast as an acorn?
• 109. Air Resistance
• Two objects will only fall at the same rate if no other force is present.
• For example: in outer space
• On Earth we have Air Resistance .
• The force that air exerts on a moving object.
• This force acts in the opposite direction of the objects motion.
• 110. Air Resistance Example
• If you drop two pieces of paper, one whole and the other crumpled up into a ball- which would hit the ground first?
• The crumpled ball because there is less air resistance.
• Air resistance pushes up as gravity pulls down .
• 111. Air Resistance
• The amount of air resistance on an object depends on the speed, size, shape and density of the object.
• 112. Projectile Motion Notes 4.2
• 113. What is a Projectile?
• Anything that is thrown or shot through the air.
• Projectiles have velocities in two directions.
• Horizontal Motion: Motion parallel to the Earth’s surface.
• Vertical Motion: The force of gravity pulling down on the object.
• 114.
• 115. Projectile Motion
• A projectile’s horizontal and vertical motion are completely independent of each other.
• Gravity will effect a projectile and a falling object in the same way.
• Therefore, if an object is dropped and thrown at the same time they will hit the ground at the same time. It does not matter that the projectile travels a farther distance.
• 116.
• 117.
• 118.
• 119.
• 120.
• 121.
• 122.
• 123. Projectile Motion Example
• http://www.phys.virginia.edu/classes/109N/more_stuff/Applets/ProjectileMotion/jarapplet.html
• 124. Circular Motion Notes 4.2
• 125. Motion along a curve
• Acceleration is a rate of change in velocity caused by a change in speed or direction!
• If you are riding a bicycle in a straight path you will not accelerate. But, if you travel around a curve the speed will accelerate because the direction is changing.
• 126. Centripetal Acceleration
• The change in velocity is towards the center of the curve.
• Acceleration toward the center of a curved or circular path is Centripetal Acceleration.
• The word Centripetal means “towards the center”.
• 127.
• 128. Centripetal Force
• In order for the bicycle to be accelerating, some unbalanced force must be acting on it in a direction toward the center of the curve.
• This force is called Centripetal Force .
• Centripetal force acts toward the center of a curved path.
• 129.
• 130.
• 131. Example of Centripetal Force
• When a car goes around a sharp curve the centripetal force is the friction between the tires and the road.
• Although, if the road is icy, the tires may lose their grip. The amount of centripetal force will not be enough to overcome the car’s inertia.
• So the car would continue to move in a straight line.
• 132. As the moon orbits the Earth, the force of gravity acting upon the moon provides the centripetal force required for circular motion. As a bucket of water is tied to a string and spun in a circle, the force of tension acting upon the bucket provides the centripetal force required for circular motion. As a car makes a turn, the force of friction acting upon the turned wheels of the car provide the centripetal force required for circular motion.
• 133. Action and Reaction Notes 4.4
• 134. Without a centripetal force, an object in motion continues along a straight-line path. With a centripetal force, an object in motion will be accelerated and change its direction.
• 135. Newton’s Third Law
• For every action, there is an equal and opposite reaction.
• For example: If you jump out of a boat the boat exerts a force on your feet pushing your forward, although your feet exert an equal and opposite force on the boat sending it backwards.
• 136. Unbalanced action - reaction pairs
• Sometimes action and reaction forces are not balanced.
• For example, if a toy truck rolls towards you, you can stop it with your hand. The action of the truck is not equal to the force of your hand.
• 137. Momentum
• While you can stop a toy truck with your hand, you would not be able to do the same for a pickup truck.
• It takes more force to stop a pickup truck than a toy truck. This is because of Momentum.
• 138. Momentum
• Momentum is the strength of motion due to the mass and velocity of the object.
• The Momentum of an object can be calculated.
• Momentum = mass x velocity
• p = m x v
• kg x m/s
• 139. Momentum Practice Problem
• A 4 kg bowling ball rolling at 6 m/s hits a bowling pin. What is the momentum of the bowling ball?
• p = m x v
• p = 4kg x 6 m/s
• p = 24 kg  m/s
• 140. Conservation of Momentum
• The momentum of an object does not change unless the mass or velocity of the object changes.
• However- momentum can be transferred from one object to another.
• The total amount of momentum does not change unless an outside force acts on the object(s).
• 141. The Energy of Motion Notes 5.1
• 142. What is Energy
• Is the ability to cause change
• Many different forms of energy
• Chemical
• Electrical
• Thermal
• Nuclear
• 143. Kinetic Energy
• The energy in the form of motion
• The amount of Kinetic Energy depends on the mass and velocity of the moving object.
• More mass = more KE
• More Velocity = more KE
• 144. Potential Energy
• The stored energy of position.
• A flower pot on a window ledge has the potential to fall.
• Potential energy depends on position.
• A flower pot on the fifth floor has the ability to cause greater change than a flower pot on the first floor.
• 145. Relationship between PE and KE
• Mechanical Energy is the total amount of Kinetic and Potential Energy in a system.
• 146. Pendulum Example
• 147. Conservation of Energy
• Energy can not be created or destroyed, it can only change form.
• 148. How do we transfer energy?
• Work is the ability to transfer energy through motion.
• The amount of work done can be calculated.
• W = F x d
• 149. Work Practice Problem
• 150. Machines Notes 7.1
• 151. What is a Machine?
• A machine is any device that makes work easier.
• Some machines are powered by engines or motors, others are simple and only require one movement.
• 152. Machines
• An ideal machine would have the work output equal to the input.
• Machines help to overcome obstacles like gravity and friction.
• 153. Simple Machines
• There are six types of simple machines
• Levers
• Pulleys
• Wheel and Axle
• Inclined Plane
• Screw
• Wedge
• 154. Compound Machine
• A combination of two or more simple machines
• A bicycle