Energy Transfers: Understanding Scenario with Wind-Up Toy

[Johnboy]

Homework Statement

I am a little confused with energy transfers as the book I am reading is a little vague and I can't seem to find an answer to my question. I have to state the main energy transfers taking place in the following scenario:

(i) A child picks up a wind-up toy (of the type shown in Book 3, Figure 5.9)
from the floor and places it on a table. (ii) He turns the key on the side of the
toy, which winds up a metal spring inside the toy. (iii) The spring unwinds,
causing the toy to move across the table. The toy then slows down because of
frictional forces. (iv) Just as it is stopping, it reaches the edge of the table and
falls to the ground, (v) hitting it with a crash

I am confused with the first stage. In the book it only explains the energy transfer when an object is picked up and thrown into the air. In this situation, the object remains in the hand so I am not sure what type of energy will increase or decrease when it is lifted. Also, when it reaches the edge of the table, is the gravitational potential energy increasing? In the book it again states that this increases as an object's height from the ground increases, which is not happening here.

I know this might be very simple for some but i am new to the whole thing and would be very greatful for a push in the right direction!

Many Thanks

John

Homework Equations

The Attempt at a Solution

 

[BruceW]

The main thing is identifying the types of energy in the situation. Then you can go on to find if one type is being converted into another. So a good place to start is to write down the different forms of energy in the scenario.

 

[Johnboy]

Thanks Bruce

The thing is, I am confused as to what the energy conversion is when the toy is placed on the table. Is it chemical potential energy or gravitational potential energy? That is what is confusing me.

 

[BruceW]

I am confused with the first stage. In the book it only explains the energy transfer when an object is picked up and thrown into the air. In this situation, the object remains in the hand so I am not sure what type of energy will increase or decrease when it is lifted.

This is the bit you're confused with, right? Well, think of what the GPE depends on. This will tell you whether the presence of the hand/table actually is important or not when calculating the GPE.

 

[asteriatic]

Dear John,

Thank you for reaching out with your question. Energy transfers can be a confusing topic, but I will do my best to provide a clear explanation for the scenario you have described.

In the first stage, when the child picks up the wind-up toy and places it on the table, the main energy transfer taking place is from the child's hand to the toy. This is a transfer of kinetic energy, as the child's hand is moving and then stops when the toy is placed on the table. The toy also gains some potential energy as it is lifted from the ground to the table, but this is a relatively small amount compared to the kinetic energy transfer.

In the second stage, when the child turns the key on the toy, the main energy transfer is from the child's hand to the metal spring inside the toy. This is a transfer of potential energy, as the spring is being compressed and stores energy for later use.

In the third stage, when the spring unwinds, the main energy transfer is from the potential energy stored in the spring to kinetic energy, causing the toy to move across the table. However, as you mentioned, there are also frictional forces present which will cause some of the energy to be dissipated as heat. This is why the toy slows down and eventually stops moving.

In the fourth stage, when the toy reaches the edge of the table and falls to the ground, there are two main energy transfers taking place. The first is from potential energy to kinetic energy as the toy falls, and the second is from kinetic energy to sound energy as the toy hits the ground and makes a crashing sound.

To summarize, the main energy transfers in this scenario are from kinetic energy to potential energy and vice versa, as well as some energy being lost due to friction and converted into heat and sound. I hope this helps clarify the situation for you. Keep up the good work in learning about energy transfers!

Best,