INTROCTION - Fill blanks for full credits.
_________ __________ is the energy of moving object. Gravitational ______________energy is the stored energy than an object has because of its position.
The amount of gravitational potential energy that an object has is shown by the formula:
PE = _________ , m is the mass on the object, h is its height above ground, g = 9.8m/s/s
The amount of kinetic energy that a moving object has is shown by the following formula:
KE = ______________, v is the speed of the object
When an object falls to the ground or rolls down a ramp, its ________________ potential energy is converted into ___________energy
if we neglect friction, we have : PE = KE
In reality friction is acting of the rolling object and some of the original energy is lost to ________ so: PE _____ KE. (is it = ? or < ? or > ? )
In this lab we will check this relation.
SKILLS: comparing, measuring, analyzing
MATERIALS: 3 solid balls of different masses, meter sticks , time watch , masking tape , incline planes ,your enthusiasm
PURPOSE: the balls will roll down a ramp, you will:
· compare the final speed (bottom speed) for different masses and heights
PROCEDURE
Step0: find the mass of the 3 balls using a pan scale in grams. Convert to kg and record the values in table 1
Step1: Set the incline plane on a thin book. Mark the departure position with a masking tape and find the height from the table to the mark.
H= _______ cm = ________m
Step2: Mark the final position, down the ramp, with another masking tape. Find the distance between the 2 tapes. D = _______cm = ________m
Step3: Place ball #1 at the top of the ramp and time how long it takes to reach the bottom.
(remember ? Average speed = total distance / total time so Vaverage = D / T
AVERAGE SPEED = (INITIAL SPEED + FINAL SPEED) / 2 or Vaverage = (V1 + V2)/2 WITH V1 = 0 (it starts at rest).
(you will derive this equation in kinematics , it only works if the acceleration is constant. And remenber: along an inclined plane
the acceleration is the acceleration due to gravity diluted, but it is constant )
Here V1 = 0 so V2 = _________ (write the algebraic epxression, use Vaverage ) . FIll TABLE1
TABLE1:
| ball | mass in kg (grams divided by 1000) | time trial 1 (s) | time trial 2 (s) | time trial 3 (s) | average time (s) | average speed (m/s) | final speed V2 (m/s) (multiply by 2 previous column) |
| 1 | ____________ | ____________ | ____________ | ____________ | ____________ | ____________ | ____________ |
| 2 | ____________ | ____________ | ____________ | ____________ | ____________ | ____________ | ____________ |
| 3 | ____________ | ____________ | ____________ | ____________ | ____________ | ____________ | ____________ |
Step7: Use your values for the final speed to find the kinetic energy at the bottom of the plane for each ball.
Record your value in TABLE 2. (Remember? KE = 0.5 mV2 , m in kg)
Step8: Use height of the ramp and the acceleration due to gravity to calculate the potential energy of each ball.
Record in TABLE 2 (remember? PE = mgH , m in kg and H in m)
TABLE2
| ball | kinetic energy (joules) | potential energy (joules) |
| 1 | ___________________________________ | ___________________________________ |
| 2 | ___________________________________ | ___________________________________ |
| 3 | ___________________________________ | ___________________________________ |
1) For each ball, compare the PE and the KE.
ball 1: the KE is : the same? Larger ? Smaller ? Than PE_________________________
Ball2: the KE is : the same? Larger ? Smaller ? Than PE_________________________
Ball3:the KE is : the same? Larger ? Smaller ? Than PE_________________________
Without ____________ PE = KE , the energy is conserved but in real life ____________________
2) Compare the PE of the three balls. As the mass increases the PE _________________
Does it make sense ? ____________________ (knowing PE = mgh)
3) Compare the final speed for the three balls. Is there a big difference ? ___________
4) Suppose there is no friction. PE=KE or mgh = 0.5 m v2
Solve for V = ________________ (use g, h, maybe m)
Does V depend on the mass ? Not matter the mass, the final speed is the _______ as long as there is no friction.
Did you get that in 3 ?
5) According to the expression of V found in 4), do you expect the speed to increase if you increase the height ? __________
check and write down your observations/
GOING FURTHER
1) complete the table, write elastic, chemical, or gravitational to identify the type of potential energy described.
| type of potential energy elastic (energy stored in an elastic object due to change in position relative to equilibrium )? chemical (energy locked in atomic bonds) ? gravitational (due to position relative to ground) ? | systems |
| ___________________________________ | fossil fuels |
| ___________________________________ | compressed spring |
| ___________________________________ | water in reservoir |
| ___________________________________ | a stretched rubber band |
| ___________________________________ | a bow drawn |
| ___________________________________ | electric batteries |
| ___________________________________ | food |
2) The amount of gravitational potential energy possessed by an elevated object is equal to the work down against _____________ in lifting it.
3) Kinetic energy equals the ______________ on the object multiplied by the distance the object moves. ( work)
4) Is the following sentence true or false ? If the speed of an object doubles, the kinetic of the object also doubles ? ___________________
(try, take any mass, any speed, find its KE, then double the speed and see what happens. use the formula for kinetic energy)
5) Express the work-energy theorem :
6) If you push a heavy refrigerator and if it doesn't slide, are you doing any work on it ?
(work is a transfer of energy. Ask your self if you increase the energy of the object if it does not move? )
7) The energy an arrow delivers to a target is slightly less than energy it had when it was flying toward the target.
What happened to the lost energy?
8) The wound spring of a toy car has 10J of potential energy. Only 8 J of this energy changes to kinetic energy as the car moves.
WHat happened to the remaining 2 J of energy?
9) The sun shines because some of its nuclear energy is transformed into ____________________ energy.
10) In nuclear reactor, nuclear energy is transformed into _________________
11) Wind can be considered a type of solar power because wind is caused by __________________
12) Calculate the increase in potential energy when a crane lifts a 2,000kg car a vertical distance of 10m. The acceleration due to gravity is 10m/s/s.
13) A 36kg girl walks to the top of the stairs that are 2 m high. How much gravitational potential energy does the girl gain ?
15) A can of soup has a mass of 0.35 kg. The can is moved from a shelf that is 1.2 m off the ground to a shelf that is 0.40m off the ground.
How does the gravitational potential energy of the can change?