Energy Conversion

The Basic Answering Technique

This science revision note aims to help your child get the proper answering technique for energy conversion.

 

But before you read on, you might want to download this entire revision notes in PDF format to print it out for your child, or to read it later.

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MUST-KNOW factors affecting gravitational potential energy:

– Mass of the object. The greater the mass of the object, the greater amount of gravitational potential energy the object possesses.

– Vertical Distance between the object and surface. The greater the distance between the object and the surface, the greater amount of gravitational potential energy the object possesses.

Take note:

You have to mention the object that possesses the energy. Simply stating the energy conversion without stating the object is insufficient.

 

Question

The diagram below shows an excavator used to demolish buildings. The metal ball is released from point Y and hits the building.

(a) Explain why when the metal ball is released from X (a point higher than point Y), the damage done by the metal ball to the building increases.

 

STEP 1

 

Identify the energy conversion and/or transfer starting from when the metal ball was released to the point when the building was hit. To make it simpler, break down each step and identify the energy conversion and/or energy transfer at each point:

  • When the ball is held at X
  • When the ball is released
  • When the ball hits the building

Remember to state the object that possesses that possesses the energy.

 

STEP 2

Take note of the comparative word “higher” in the question. Remember to compare in your answer by using words like “more” and “greater”.

 

FINALLY, put your answer together

At X, metal ball is at a higher position. The metal ball has more gravitational potential energy.

When the metal ball is released, more gravitational potential energy of the ball is converted to more kinetic energy.

When the metal ball hits the building, more kinetic energy of the metal ball is converted to more kinetic energy of the building, causing the destruction to be greater.

 

Take note:

Those highlighted in yellow are the description of a situation.

Use comparative words such as more

 

 

🥳Congratulations! 🥳

You have just completed part (a), the basic explanation for energy conversion. It is time to answer part (b)!

 

(b) Other than swinging the ball higher, what can be done to increase the damage done to the building? Explain why.

STEP 1

Identify the factors that affect gravitational potential energy.

 

STEP 2

In part (b), the factor is the “mass”.

Repeat step 2 as shown in part (a).

 

FINALLY, put your answer together

Increase the mass of the metal ball. When the mass of the metal ball is increased, the metal ball has more gravitational potential energy which is converted to more kinetic energy when the metal ball is released. When the metal ball hits the building, more kinetic energy of the metal ball is converted to more kinetic energy of the building, causing the destruction to be greater.

 

Take note:

Those highlighted in yellow are the description of a situation.

Use comparative words such as more

 

Common mistakes

Wrong answer: Gravitational potential energy is converted to kinetic energy.

Failure to state the object that possesses the energy makes your answers unclear. Remember to state gravitational potential energy of the (object) is converted to the kinetic energy of the (object).

 

 

Let’s try out another question!

 

Jacob and Dylan each held a basketball in their hand, as shown in the diagram below. Both basketballs are identical. They then took turns removing their hands from under the ball to let it drop naturally. They compared the loudness of the sound made when the basketballs landed on the floor.

Whose basketball made a louder sound? Explain why.

 

STEP 1

Identify the energy conversion that takes place for the balls to make a sound when they land on the floor.

Gravitational potential energy (of the basketball) —> Kinetic energy (as the basketball is falling) —> sound energy (when the basketball hits the floor)

 

STEP 2

Identify which type of energy was changed and how it was changed.

To do this, you have to identify what is the changed variable when Jacob and Dylan were letting the ball drop.

Looking at the diagram, you can see that Dylan’s basketball is higher above the ground than Jacob’s basketball. Hence, the height of the basketball is the changed variable.

 

So which type of energy does the height of the basketball affect? Gravitational potential energy.

The greater the height of the basketball, the greater the gravitational potential energy. Therefore, Dylan’s basketball has more gravitational potential energy.

 

STEP 3

Explain how the change in Step 2 affects the sound made when the basketballs land on the floor. Use the energy conversion you identified in Step 1 in your explanation.

More gravitational potential energy (of the basketball) —> More kinetic energy (as the basketball is falling) —> More sound energy (when the basketball hits the floor)

Therefore, Dylan’s basketball made a louder sound when it landed on the floor.

 

FINALLY, put your answer together

Question: Whose basketball made a louder sound? Explain why.

Answer: Dylan’s basketball made a louder sound.

Evidence: Dylan’s basketball was higher above the floor compared to Jacob, so the basketball had more gravitational potential energy.

Reasoning: As the basketball in Dylan’s hands is falling, more gravitational potential energy is converted to more kinetic energy of the basketball.

When the ball hits the floor, more kinetic energy of the basketball is converted to more sound energy. 

 

Take note:

Those highlighted in yellow are the description of a situation.

Use comparative words such as more

 

 

Common mistakes

 

Wrong answer: Dylan’s basketball made a louder sound. Dylan’s basketball was higher above the floor compared to Jacob, so it had more gravitational potential energy. More gravitational potential energy is converted to more kinetic energy and more sound energy when the ball hits the floor.

 

Teachers’ comments:

The explanation is unclear. When you say “more gravitational potential energy (GPE) is converted to more kinetic energy (KE) and to more sound energy (SE)”, The student is informing the teacher GPE is converted to more KE and SE at the same time. That is not the correct sequence.

 

Hence, we recommend your child to split your explanation into separate sentences to make it clearer:

1) More gravitational potential energy of the ball is converted to more kinetic energy

2) More kinetic energy of the ball is converted to more sound energy when the ball hits the floor.

 

You might want to use the words “and then to” to show the sequence of energy conversion in different situations.

 

 

Read the revision notes on common mistakes on energy conversion for detailed explanations.

>> https://scienceshifu.com/common-mistakes-on-energy-conversion/

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