Introduction

Welcome back to our Examination Paper Analysis series!

In this article, we will be analysing a question on the topic of Forces from the 2015 Nanyang Primary School (NYPS) P5 SA2 Examination Paper. We will also be discussing how to phrase your answers the right way for questions involving energy conversions, and the different effects and types of Forces.

## Let’s Take A Look At This Question

Source: Nanyang Primary School – 2015 P5 SA2 Examination Paper [Q44]

## Let’s Analyse Part (A)

Source: Nanyang Primary School – 2015 P5 SA2 Examination Paper [Q44]

Part (a) is asking us to explain why the marble stopped rolling. First of all, we have to understand why the marble even rolled in the first place. The marble rolled because there was a push force applied to it.

When the marble is pushed, the marble starts moving. What kind of energy will this marble possess? Kinetic energy!

We learned that kinetic energy is a form of movement energy. Throughout the ball’s movement, we also learned that kinetic energy is going to be converted into two other forms of energy.

Do you know what those two other forms of energy are? The first one is heat energy and the other one is sound energy.

Why is kinetic energy converted into heat energy and sound energy? It is because of this force called friction.

📌 Energy Conversion Due To Friction 📌

Because of friction, kinetic energy is converted into heat and sound.

Eventually, there will no longer be any kinetic energy, so the marble will come to a stop.

## Suggested Answers For Part (A)

If we were to use energy to explain:

“All of the kinetic energy of the marble had been converted into heat energy and sound energy. The marble no longer possessed any kinetic energy and stopped rolling.”

On the other hand, we can strictly use forces to explain our answer:

“There was friction involved. Because of the friction between the surface of the marble and the floor, the marble came to a stop.”

## Let’s Analyse Part (B)

Source: Nanyang Primary School – 2015 P5 SA2 Examination Paper [Q44]

If we want to make the marble roll over a longer distance, there are a few things we can do.

One way we can make the marble roll over a longer distance is to increase the push force that’s acting on the marble. We can exert a greater push force on the marble, and this would allow the marble to possess more kinetic energy.

What else can we do if we don’t want to push the marble with greater force?

Ask yourself: what is stopping the marble from moving? As discussed earlier, there is kinetic energy being converted into heat and sound energy because of this force called friction.

If we want the marble to move for a longer distance, another thing we can do is to reduce the amount of friction present. We can add lubricants.

A good example of a lubricant would be oil. Oil is a lubricant, and it will reduce friction.

📌 Remember This When Using The Keyword ‘Friction’ 📌

When using the keyword friction, we must always remember to write “between [one thing] and [something else]”.

In this case, the friction between the marble and the floor is reduced.

If we don’t want to use oil, another substance that can help reduce friction is a substance that can smoothen surfaces.

If you’re thinking about powder, you are right! What we can do is to put powder on the floor.

When we put powder on the floor, it will eventually become smoother and will help reduce friction between the surface of the marble and the floor as well.

## Suggested Answer For Part (B)

1. Push the marble with a greater force.
2. Apply oil on the floor. Oil acts as a lubricant, reducing the friction between the surface of the marble and the floor.
3. Add powder on the floor to reduce the friction between the surface of the marble and the floor. This is because powder makes the floor smooth.

## Let’s Analyse Part (C)

Source: Nanyang Primary School – 2015 P5 SA2 Examination Paper [Q44]

What we have learned so far in terms of the effects of forces is that they’re different from the types of forces.

Let’s do a quick recap of the four types of forces that you have learnt so far:

• Gravitational force
• Frictional force
• Magnetic force
• Elastic spring force

I am sure you also know that these types of forces are different from the five effects of forces. Let’s do a quick review of these five effects:

1. When a force is applied to a stationary object, it can cause the object to start moving.
2. If the object is already moving, a force can cause a moving object to stop moving.
3. If an object is already moving and a push force is applied to it towards the same direction, the object can move faster. And if a push force is applied to a moving object in the opposite direction, the object can move slower. In essence, the third effect involves a change in speed.
4. If a push force is applied to an object in a different direction, it can cause the object to change direction.
5. If a force is applied to an object, it can cause the object to change shape.

Which of these effects of forces can we apply to the scenario given?

Let’s read the question again. It is asking for two possible effects on the moving ball when a force is exerted on it.

I would like us to focus on this keyword, moving. A common misconception is that the force acting on the ball caused it to start moving.

Is it possible to use this statement here: “to start moving”? Is that one of the effects of forces that we can write as our answer? No!

That is because, as the question states, the ball is already moving in the first place!

## Suggested Answers For Part (C)

1. The force acting on the moving ball caused it to stop moving.
2. The force acting on the moving ball caused it to move faster.
3. The force acting on the moving ball caused it to move slower.
4. The force acting on the moving ball caused it to change direction.

## Conclusion

I hope that you now have a clearer understanding of how friction works and what you can do to reduce friction between surfaces after reading this blog post.

I have also taught you the importance of referring to the information provided in the question. This prevents you from rushing into writing down “possible” answers that are wrong!

Check out our other articles on Forces and continue to keep a lookout for more articles! 🙂

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