A: Potential or kinetic energy? B: Potential or Kinetic energy?
Potential and Kinetic Energy
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Potential and Kinetic Energy • Energy: is the ability to do work • Work is being done whenever some physical force is being used to move an object some distance
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Potential and Kinetic Energy. Energy: is the ability to do work Work is being done whenever some physical force is being used to move an object some distance. Energy means that birds can fly, tigers can roar, wind can blow, sun can shine, cars can go fast, - PowerPoint PPT Presentation
Transcript of Potential and Kinetic Energy
Potential and Kinetic Energy
• Energy: is the ability to do work
• Work is being done whenever some physical force is being used to move an object some distance
Energy means that • birds can fly,• tigers can roar, • wind can blow, • sun can shine, • cars can go fast, • factories can make things, • light bulbs can glow and • your computer can work. Without energy, there would be nothing: no life, no
movement, no light, … nothing
Energy• All objects contain energy in one form or another• Can take the form of
– Motion -Sound– Position - Electricity– Heat– Light
• It can never be destroyed• It can only be converted from one form to
another
Kinetic Energy= the energy an object possesses
because of its motion
• The amount of Kinetic energy is dependent on the mass of the object in motion and it’s velocity.
• Objects "tend to keep on doing what they're doing"
• In fact, it is the natural tendency of objects to resist changes in their state of motion.
• Without some outside influence, an object in motion will remain in motion and an object at rest will remain at rest.
This tendency to resist changes in their state of motion is described as inertia
Cardboard and a Coin placed on an Empty Tumbler Flick the cardboard with the finger. What do you observe? The coin drops into the tumbler. When we flick the cardboard the cardboard moves fast whereas the coin continues in its state of rest and hence drops into the tumbler.
Cardboard and a coin placed on an empty glass
Flick the cardboard with the finger. What do you observe? The coin drops into the tumbler. When we flick the cardboard the cardboard moves fast whereas the coin continues in its state of rest and hence drops into the glass.
So it is clear that objects continue to remain in their state of rest or of uniform motion until an external force is applied.
Potential Energy
• The energy of position• The amount of energy contained in an object
at rest
Potential or Kinetic Energy?
• Moving car• Tree branch• Bent car fender• Balloon filled with air• Balloon squirting around room• Person inside a moving car
• What type of energy does the space shuttle have at lift off?
• The water at the top has potential energy
• When water falls to a lower level, the potential energy is converted to kinetic energy.
Velocity & Acceleration
Some Review
Defining Velocity
Kinetic energy was – KE=1/2 (mass) (velocity)2
•Describes both the rate and direction of the motion
•If an object speeds up or slows down in the given direction we say there is a change in velocity
VELOCITY AND SPEED
Velocity is a measure of how fast an object is traveling in a certain direction.
•Example: A bus traveling 15 m/s increases its speed to 20 m/s
•The speed changed so the velocity changed
•The bus changes direction and goes east. Since the direction changed, so did the velocity
Car on a circular track = may have constant speed, but cannot maintain a constant velocity
as it’s direction is always changing.
VELOCITY AND SPEED
– Speed is a measure of how fast something is moving, but there is not a directional element to it
– Is the distance on object moves per time or how fast something is moving without direction
– Speed = Distance ÷ Time (S=D ÷ T)
– If speed changes, so does the velocity
VELOCITY
Velocity = distance ÷ time
The units we use are m/s and d is distance.
ACCELERATION
• Acceleration is the change in velocity per unit of time.
• An example of this is when you travel in your car.
• Your velocity is not constant throughout the entire trip as you slow down and speed up as necessary.
• A positive acceleration means that you are speeding up and a negative acceleration means that you are slowing down.
ACCELERATION
• Acceleration has the formula:
Acceleration = (Final Velocity) – (initial velocity) (Final time) – (Initial time)
OR(time it takes to change velocity)
A = vf – vi = ∆v ∆ means “change in” tf – ti ∆t
Acceleration has the units of (distance unit)/(time unit) Ex: m/s2 or mi/h2
ACCELERATION
• Example acceleration problems
• Calculate the acceleration of an object with:» Initial Velocity : 0.0m/s» Final Velocity: 14m/s» Time 4.0s
» A = 14m/s – 0.0m/s4.0s
A = 3.5m/s2
ACCELERATION
• A car stops from a velocity of 55m/s in 15 seconds. What is the cars acceleration? Is the car speeding up or slowing down?
• A = 0 – 55m/s -55m/s 15 s 15s
A = -3.7m/s2
Car is slowing down
