experiment 5 kinetic and potential energy pre lab questions explain how speed and weight affect

1. Speed and weight both affect the amount of kinetic energy. Kinetic energy is directly proport

Experiment 5 kinetic and potential energy pre lab questions...

Experiment #5: Kinetic and Potential Energy Pre-Lab Questions 1. Explain how speed and weight affect the amount of kinetic energy. 2. Identify three examples of items that can store potential energy. 3. How can energy be transferred back and forth between kinetic energy and potential energy? 4. Identify one example of how potential chemical energy is used. 5. Name two kinds of energy that potential and kinetic energy can create. 6. How does kinetic energy apply a force to something else? 7. What type of energy is created when a brick falls from the top of a wall? 8. Explain how kinetic energy can be changed into potential energy. OVERVIEW: This lesson is to help students more fully understand the relationship between Potential and Kinetic energy. Students should already know the definitions for work and mechanical energy. PURPOSE: Students will observe and record the amount of work done by the three different marbles rolling down an inclined plane and hypothesize about the reasons for the differences. OBJECTIVES: Students will: 1. Discover that the larger the mass, and the higher an object is raised, the more energy is stored. 2. Measure the differences in inches and/or centimeters. 3. Compute the average distances. 4. Make predictions, record observations, and create hypotheses. MATERIALS: - 3 marbles or balls (different sizes &/or weights) - inclined plane - ruler - milk carton PROCEDURES: 1. Roll three different sized marbles down an inclined plane. 2. Place the bottom section of a milk carton at the bottom of the ramp to catch the marble and measure the distance that it moves the carton. 3. Repeat five times and take the average distance. 4. Repeat the process using the second and third marbles. DATA AND OBSERVATIONS: Post-lab Questions: 1. What is work? 2. What is mechanical energy? 3. Which marble/ball could have more mechanical energy? 4. If I put the marbles/balls up on the inclined plane, would they have energy? Why? 5. Which marble had the most kinetic energy? Why? 6. What would happen if the smaller marble was let go at twice the height of the larger one? Why? 7. What are some examples of storing and using energy in our environment? 8. What factors affect the amount of work an object can do?

Transcript

00:01 So all the objects start at the same height and they all have the same mass and one more thing is they roll without slipping so they have their mechanical energy conserved so we know that by conservation of mechanical energy we mean that the total energy at initial position must be equal to the total energy at the final position and if we call this as our initial position let's call it number one so so, subscript 1 relates to all the energies corresponding to this place.

00:36 And when the object moves to the base, we call it point 2, which is the total energy corresponding to this point.

00:44 Now we can see here that all the objects start from rest.

00:48 So that means at this point, they will have the potential energy, but there's no kinetic energy.

00:55 So we can get rid of this part.

00:59 And this point if we set y equal to zero here so y2 becomes zero and y1 over here becomes h so we can get rid of the potential energy at this point so we have mechanical energy is equal to kinetic energy and also we see that the object rolls as well as it moves through the slope so it will have the rotational kinetic part and the translational kinetic part so we'll be using f equals m a for the translational part and for the rotational part we'll be using tau equals i times alpha so that's when we do the force calculation and as we mentioned for kinetic energy calculation we'll have total kinetic energy which is a combination of translational kinetic energy plus rotational kinetic energy.

02:05 So this translational part is easy.

02:08 It's just half of mv squared where v is the velocity at this point.

02:15 So let's call it vcm and rotational part is just half of i cm omega squared where omega is the angular velocity at this point.

02:30 So we can combine all those together and and see what we get.

02:35 So first of all before doing that, we see that this moment of inertia is different for different objects.

02:43 And let's call this i -c -m, which is equal to cmr squared, where c is a number, and that will vary depending on what object we're choosing.

02:58 For example, if we're choosing solid cylinder, then c is 2 over 5, and so on and so forth.

03:03 So yeah, so if we actually use this equation now, as we mentioned that i will be chosen as cmr squared.

03:15 So we start with the energy conservation and as we mentioned that we got rid of the kinetic part.

03:21 So this is zero and at this point this one is zero.

03:25 So at the top we have the potential energy.

03:29 So mgh is the potential energy and the kinetic part is half mv squared.

03:34 Plus i omega square half i omega square where i is cmr squared so that's what we wrote and if we combine everything together we see that it's half v times one plus c from there if we write b squared in terms of the other parameters we see it's 2gd divided by 1 plus c so there will be m here so let me write it here and we got rid of ms on both sides right so yeah we know v now and we can figure out which has the highest velocity from there and if an object has the highest translational velocity that will take the minimum amount of time to reach at the bottom because they will have the highest average velocity as well so highest v means minimum time and if we look at this equation carefully, we see that 2gh, this part is constant.

04:42 The only thing that's changing here is c.

04:45 So that means the velocity is inversely proportional to c.

04:50 So if c increases, velocity decreases.

04:53 Now, we know that for solid sphere, it's 2 over 5.

04:56 For solid cylinder, it's half.

04:58 Holosphere, it's 2 over 3, and hollow cylinder it's 1.

05:01 So whichever has the highest c will have the lowest.

05:07 Velocity and hence the maximum time and whichever has the lowest c will have the highest velocity and hence the minimum time so we see that from this chart the solid sphere has the lowest amount of c which means it will have the highest velocity so it will take the minimum time to reach the bottom so that's why from our diagram in the question a will be the solid sphere then following that will be b and then it will be c and then it will be d so that's the increase in increasing order of time so in this way the time is increasing that's increasing time so this way it's decreasing time so for part b we need to figure out which has the greatest kinetic energy now part b is easy because it will have the same kinetic energy and the reason we say that is hidden in this equation because we see that the kinetic energy at the bottom is equal to the potential energy and since all the objects have the same mass so the potential energy is concerned or the potential energy is constant for all of the objects so if the potential energy is constant then kinetic energy must be constant because we have a we have an equality sign in between them so for all the objects we'll have the same amount of kinetic energy so that's why have same kinetic energy.

06:44 In part c we have to figure out which has the greatest rotational kinetic energy at the bottom of the ramp.

06:51 So for rotational part it's just half of i omega squared and that'll change because we have a c factor here which depends on different objects...

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