law of conservation of energy the total amount of energy in the system remains constant it can only...
TRANSCRIPT
![Page 1: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/1.jpg)
Law of Conservation of Energy
The total amount of energy in the system remains constant
• It can only be converted from one form to another
BUT• No new energy can be created• It can never be destroyed
![Page 2: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/2.jpg)
Potential and Kinetic Energy
• Energy: is the ability to do work
![Page 3: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/3.jpg)
Potential Energy
• The energy of position• The amount of energy contained in an
object at rest
![Page 4: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/4.jpg)
Determining Potential Energy
• By its position and its weight (mass X gravity)
PE = (mass)(gravity)(height) = mgh• where m is mass in kg• g is the force of gravity = 9.8 m/s2
• h is the height• The SI unit that represents potential
energy is the Joule (J) (kg m2/s2).
![Page 5: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/5.jpg)
Examine an example of potential energy
A flower pot with a mass of 15 kg is sitting on a window sill 15 meters above the ground. How
much potential energy does the flower pot contain?
• PE = (mass)(gravity)(height)• = (15 kg)(9.8 m/s2)(15 m)• = 2205 kg m2/s2
• = 2205 J• = 2.2 x 103J
![Page 6: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/6.jpg)
Kinetic Energy
• SO….
Once force is applied to an object, the object is set into motion.
• A moving object is said to contain kinetic energy or energy of motion.
• The amount is related to the mass of the object in motion and it’s velocity.
![Page 7: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/7.jpg)
Calculating kinetic energy
If we know the mass of an object and its velocity we can determine the amount of kinetic energy possessed by using the following formula:
kinetic energy = 1/2 (mass of object)(velocity of object)2
or KE = 1/2 mv2
or KE = 0.5mv2
The SI unit for kinetic energy is the Joule (J).
A Joule is kg m2/s2
![Page 8: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/8.jpg)
A bicycle with a mass of 14 kg traveling at a velocity of 3.0 m/s east
has how much kinetic energy?
KE = 0.5mv2
= 0.5(14 kg)(3.0 m/s)2
= 0.5(14 kg)(9.0 m2/s2)
= 63 kg m2/s2 = 63 J
![Page 9: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/9.jpg)
![Page 10: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/10.jpg)
• What type of energy does the space shuttle have at lift off?
![Page 11: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/11.jpg)
![Page 12: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/12.jpg)
Conversion of Potential to Kinetic Energy
• In this picture both kinds of energy are evident. Can you point them out?
![Page 13: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/13.jpg)
• The water at the top has potential energy
• When water falls to a lower level, the potential energy is converted to kinetic energy.
![Page 14: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/14.jpg)
FORCES
• The term force refers to the interaction of objects and their environment.
• All forces are exerted on one object by another object.
• Forces have both size and direction and are normally classified as “pushes or pulls”.
• All forces have both size and direction
![Page 15: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/15.jpg)
Gravity – most familiar force
• Gravity is the basic force of attraction that is spread throughout the universe. Gravity pulls objects towards each other.
• Gravity on earth pulls you and all objects towards the earth.
• You must overcome gravity each time you lift something.
• Gravitational force on earth is 9.8m/s2
• Other forces –– Buoyancy -Friction– Electricity -Pressure
![Page 16: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/16.jpg)
Calculating Force
The relationship between an object's mass m, its acceleration a, and the applied force F
Force =(mass)(acceleration) or F = ma
• The SI units for force is the Newton (N)
A Newton is equivalent to the units:
N = kg x m s2
![Page 17: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/17.jpg)
Example
• An object with a mass of 15.0 kg is moving with an acceleration of 25.0 m/s2. What is the force acting on that object?
F = ma
= (15.0 kg) x 25.0m/s2) = 375 kg• m/s2
= 375 N
![Page 18: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/18.jpg)
Another Force - Weight
• Weight is a force applied to an object as a result of gravity.
• Weight = mass x (gravitational force)
Fw = (m) (g)
• On earth, the force of gravity is nearly constant = 9.8 m/s2
![Page 19: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/19.jpg)
Mass vs. weight Understand the difference
Mass is: Weight is: A measure of the amount of
matter in an object.
A measure of thegravitational force on anobject.
Always constant for anobject no matter where theobject is in the universe.
Varied depending on wherethe object is in relation tothe Earth or any other largebody in the universe.
Expressed in kilograms,grams, and milligrams.
Expressed in Newtons (N).
![Page 20: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/20.jpg)
Weight
• It is different depending on where the object is located and the amount of gravity acting on it.
• Weight is expressed in Newtons (N) • Weight of an object can be determined by
the following formula
Weight = (mass) (gravity)OR
Fw = (m)(g)
![Page 21: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/21.jpg)
Example
If an object has a mass of 75 kg on earth, what is it’s weight?
Fw = (m)(g) = (75 kg) x (9.8 m/s2)
= 735 kg • m/s2
= 735 N
= 740 N
![Page 22: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/22.jpg)
Re-Arrange the Formula
Solve for weight
Fw = (m)(g)
Solve for mass
m= Fw ÷ (g)
Solve for gravity
g= Fw ÷ (m)
![Page 23: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/23.jpg)
How Energy Relates to Work
Energy - the ability to do workWork - a measure of how productive an applied force is
![Page 24: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/24.jpg)
Work
• Work is the product of the force applied to an object time the distance through which the force acts
• EXAMPLES OF WORK– Lifting a book– Pulling a cart– Pushing a door open
• Sometimes there are easy ways and hard ways to do the same amount of work.
![Page 25: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/25.jpg)
Work
• The formula for work is:Work = (force) (distance) or W = Fd
The unit for work is the Joule
J = N * m = kg *m2
s2
It is important that you understand that all units used in the equation are in Kg, m and seconds. The problem will not be accurate (or correct) if the units are not in this form.
![Page 26: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/26.jpg)
Example
• A book weighing 3.0N is lifted 5m. How much work is done?
W = Fd
W = (3.0N) (5m)
W = 15J
![Page 27: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/27.jpg)
You need to rearrange the equation to get force.
F = W ÷ d
Rearrange for distance
d = w ÷ F
![Page 28: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/28.jpg)
Using Simple Machines to do Work More Easy
Devices that allow us to perform the same amount of work more
easily.
![Page 29: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/29.jpg)
Simple Machines Work in One of 3 Ways
1. Can take the force exerted by the individual and redirect it
2. Can turn a small effort or force into a larger force (mechanical advantage)
3. Can magnify the distance that a force acts on
Machines do not reduce the amount of work needed to perform a task, they
reduce the effort needed from the user.
![Page 30: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/30.jpg)
3 Kinds We Will Consider
1. Lever
2. Inclined Plane
3. Pulley
![Page 31: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/31.jpg)
The Lever
• Is a narrow beam that rotates around a single point called the fulcrum
• By placing an object to be moved, called the load, at one point on the beam and by applying an effort at another point the object can be moved more easily
![Page 32: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/32.jpg)
1st Class Lever
• 1st class – where the fulcrum lies between the load and the effort
EffortLoad
Fulcrum
![Page 33: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/33.jpg)
![Page 34: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/34.jpg)
2nd class lever
• 2nd class levers where the fulcrum lies at one end and an effort is placed at the other end.– The load lies in between Effort
Load
Fulcrum
![Page 35: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/35.jpg)
![Page 36: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/36.jpg)
3rd Class Lever
• 3rd class lever – where the effort is applied between the load (W) and the fulcrum
Fulcrum
Effort
Load
![Page 37: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/37.jpg)
![Page 38: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/38.jpg)
Review of Levers
1st Class LeverLoad – Fulcrum – Effort
2nd Class LeverFulcrum – Load – Effort
3rd Class LeverFulcrum – Effort - Load
![Page 39: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/39.jpg)
Formula for Levers
Effort X distance from the fulcrum = weight X distance from the fulcrum
The ability of the lever to help perform work is dependent on the length of the lever and on the mass applied to the lever.
Too heavy of a mass or too long of lever the lever will break.
![Page 40: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/40.jpg)
How much mass can a lever handle?
Apparatus for lab looks like this:
![Page 41: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/41.jpg)
Inclined Plane
• Device designed to reduce the force needed to raise an object.
• For example, pushing a load up a ramp onto a platform requires less force than lifting the load onto the platform.
• Ramps and steps are forms of inclined planes.
![Page 42: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/42.jpg)
Screw
• Screw is an inclined plane wrapped in a spiral around a shaft.
![Page 43: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/43.jpg)
Wedge
• Wedge is actually 2 inclined planes joined back-to-back
• The planes exert lateral forces to split the piece of wood
![Page 44: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/44.jpg)
Remember!
An inclined plane does not reduce the amount of work being done –
It simple reduces the force necessary to complete that work by creating a mechanical advantage.
![Page 45: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/45.jpg)
Pulleys
• is a wheel over which a rope or belt is passed for the purpose of transmitting energy and doing work.
![Page 46: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/46.jpg)
Pulleys
Reduce the effort to raise an object or it redirects the applied force, depending on the type of pulley.
![Page 47: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/47.jpg)
Velocity & Acceleration
Some Review
![Page 48: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/48.jpg)
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
![Page 49: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/49.jpg)
VELOCITY AND SPEED
Velocity is a measure of how fast an object is traveling in a certain direction.
– Example: A plane moving at 600mph to the north has a velocity.
– Important to realize that for you to use velocity, you must have a direction!
– Speed is a measure of how fast something is moving, but there is not a directional element to it.
![Page 50: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/50.jpg)
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
– Speed = Distance X Time (S=D x T)
– If speed changes, so does the velocity
![Page 51: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/51.jpg)
VELOCITY
Velocity = distance ÷ time
The units we use are m/s and d is distance.
Rearranging the formulas for all possibilities:V= d/td = vtt = d/v
![Page 52: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/52.jpg)
VELOCITY
• What is the velocity of a car that travels 100m in 2 hours?
V = d/t 100.m/2h = 50.0m/h
A car travels 65.0m/h for 3.00 hours how far did it go?
d = vt (65.0m/h) (3.00h) = 195m =
How long would it take a car to travel 200 miles at a velocity of 70m/h?
t = d/v t = 200m/70m/h t = 2.9h = 3hrMake sure you work your problems so that units cancel out.
![Page 53: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/53.jpg)
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.
![Page 54: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/54.jpg)
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 ∆ tAcceleration has the units of (distance unit)/(time unit) Ex: m/s2 or mi/h2
![Page 55: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/55.jpg)
ACCELERATION
• Example acceleration problems
• Calculate the acceleration of an object with:» Initial Velocity : 0.0m/s» Final Velocity: 14m/s» Time 4s
» A = 14m/s – 0m/s
4s
A = 3.5m/s2
![Page 56: Law of Conservation of Energy The total amount of energy in the system remains constant It can only be converted from one form to another BUT No new energy](https://reader036.vdocuments.mx/reader036/viewer/2022070306/5519e43b55034691578b4654/html5/thumbnails/56.jpg)
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