Energy Conversion

Elastic Potential Energy to Kinetic Energy

This science revision note aims to help your child

– identify the energy conversion taking place

– Write out the answer using the proper scientific keywords.

– Learn how to combine frictional forces concept with energy conversion concept in this question.

 

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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Shayna created a setup as shown below.

She pushed the ball to completely compress the spring and then released the ball to let it roll across the floor. When the ball stopped rolling, she measured the distance travelled by the ball. Afterwards, she added some oil to the floor and repeated the same experiment.

How will the distance travelled by the ball be affected after she added oil to the floor? Using energy conversion, explain why.

 

STEP 1

Identify the energy conversion that takes place for the balls to roll across the floor and then come to a stop.

Elastic potential energy (in the spring) —> Kinetic energy (in the ball as the ball is rolling) —> heat energy (due to friction between the ball and 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. The changed variable is the presence of oil on the floor.

So which type of energy does the oil on the floor affect? Heat energy due to friction between the ball and the floor.

 

How does oil affect heat energy? Oil is a lubricant, which reduces friction between the ball and the floor. A decrease in the amount of friction decreases the amount of kinetic energy that is converted to heat energy. Therefore, when there is oil on the floor, less kinetic energy is converted to heat energy due to friction.

 

STEP 3

Explain how the change in Step 2 affects the distance travelled by the ball. Use the energy conversion you identified in Step 1 in your explanation.

Elastic potential energy (in the spring) —> Kinetic energy (in the ball as the ball is rolling) —> Less heat energy (due to friction between the ball and the floor)

Therefore, when there is oil on the floor, there is more kinetic energy left in the ball for the ball to travel a longer distance.

 

FINALLY, put your answer together

Question: How will the distance travelled by the ball be affected after she added oil to the floor? Using energy conversion, explain why.

Answer:

After she added oil to the floor, the distance travelled by the ball will increase.

Oil reduces the friction between the ball and the floor.

When the compressed spring is released, the elastic potential energy in the spring is converted to kinetic energy in the ball. Less kinetic energy in the ball is converted to less heat energy due to less friction. Therefore, there is more kinetic energy left in the ball to allow it to travel a longer distance.

 

Take note:

Those highlighted in yellow are the description of a situation.

Use comparative words such as less or more

 

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

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

 

Read the revision note on the challenging question for energy conversion

>>> https://scienceshifu.com/science-challenging-question-on-energy-conversion/

 

Common mistakes

Wrong answers:

  • Less kinetic energy is lost to friction
  • Less heat energy is produced due to friction.

Energy cannot be produced or destroyed. Hence, you cannot use the terms “lost” or “produced” when talking about energy. Energy can only be converted from one form to another.

 

Incomplete answer: There is less frictional force between the ball and the floor, so the ball can travel a longer distance.

The concept of frictional force is correct. However, the question specifically asks you to explain using energy conversion. Hence the answer is incomplete.

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Talk again soon!

Andy Ling

Guiding your child to be the master of science concepts

 

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