Skip to main content

3 Common Mistakes in P6 Forces

By


3 COMMON MISTAKES IN FORCES: 

*Apologies that the alignment of this page is off & I can't seem to get it adjusted for now. If you want a downloadable worksheet, PM us at isuninfo@gmail.com* 

1. Gravitational force (GF) vs Gravitational Potential Energy (GPE)











 Example 1
The ISUN warriors were playing at the corridor with a wooden ball. Xavier accidentally threw a ball and it travelled in the path as shown below rolling to a stop. 


Which one of the following statements is correct?
1)      Gravity acted on the ball only when it travelled from Q to R.
2)      There are no other forces acting on the ball from P to Q except gravity.
3)      The amount gravity acting on the ball when it travelled from P to R is the same.
4)      The amount of gravity acting on the ball increased when the ball travelled from P to Q and decreased when it dropped from Q to R.

Common Answer: 4
Why is it wrong?
Students often confused gravitational potential energy (GPE) with gravitation force (GF).
Option 4 is correct if we changed it to: “The amount of GRAVITATIONAL POTENTIAL ENERGY acting on the ball increased when the ball travelled from P to Q and decreased when it dropped from Q to R”

Actual Answer: 3
Use the strategy: GF = weight. Now, re-read option 3: “The[amount gravity acting on] (WEIGHT of) the ball when it travelled from P to R is the same.”

Example 2

The diagram below shows the path of a football after Caeden had kicked it.


Which one of the follow graphs shows the relationship between the height of the ball above the ground and its gravitational force acting on it? 




Common Answer: 1 
Why is it wrong?
Grapph 1 is for GPE 

Actual Answer: 2 
Use the strategy: GF = weight. The[amount gravity acting on] (WEIGHT of) the ball at any point is the same.

Apply the strategy that I just taught you: “GF = Weight”

Example 3
Max and Woon Seng went for an adventure camp. The diagram below shows the 2 boys, A and B as they slide down the zipline from 2 different heights.


Which one of the following statements best describes the gravitational force possessed by the 2 boy of similar built and at similar starting point but different height?

1)      Both boys have no gravitational force acting on them 
2)      Boy A has less gravitational force acting on him than Boy B
3)      Boy A has more gravitational force acting on him than Boy B
4)      Both boys have similar amount of gravitational force acting on them


Did you get it? The answer is 4!
The boys have similar built thus their weight is the similar and thus similar gravitational force is acting on it.


2. Frictional Force 













Example
Block M is a bar magnet. It was placed on a flat glass table as shown below. A copper block was attached to the bottom of the table. Block M was given a push to move along the table. 

 
(a)    Which of the force(s) below must the push overcome in order for Block M to move along the table? 

1)      Frictional only 
2)      Frictional and Magnetic only 
3)      Frictional and Gravitational only 
4)      Frictional, Gravitational and Magnetic

Common mistake: 3
Actual answer: 1

Students know that there are frictional and gravitational force acting on the object but they didn’t relate to what the question wants. The push force needs to overcome frictional force between the table and the block M to move across the table from left to right (FF is acting on the block in the opposite direction).



(b)    Which of the following force(s) is/are acting on block M when it has come to a complete stop? 

1)      Frictional only 
2)      Gravitational only 
3)      Frictional and Gravitational only 
4)      Frictional, Gravitational and Magnetic 
Common mistake: 3
Actual answer: 2

Recall: There is no friction acting on the object when it is stationary.


(c)     Which of the following force(s) is/are acting on block M as it move along the table?

1)      Frictional only 
2)      Frictional and Magnetic only 
3)      Frictional and Gravitational only 
4)      Frictional, Gravitational and Magnetic

Actual answer: 3

Recall: When the object is moving, there is friction between the block M and table top. Gravitational force acts on an object all the time.



(d)    Design a question using the above diagram such that the answer is 4. 

Question: _______________________________________________________________________

________________________________________________________________________________

1)      Frictional only
2)      Frictional and Magnetic  only
3)      Frictional and Gravitational only
4)      Frictional, Gravitational and Magnetic

(4)

Possible question,
If the copper block was replaced with a cobalt block, which of the following force(s) is/are acting on block M as it move along the table?


3. Elastic Spring Force 



Are you having the same answer as the student too?
Read again! The question is asking for final length but the graph shows extension!



Hope that the above tips will help your child! :)


THE WAY THAT IT IS BROUGHT ACROSS TO YOUR CHILD IS IMPORTANT! 

ENGAGE THEM! These questions are pasted around our place and they are to solve it as a team. They made mistakes & they learn from it. 

What happens if its just delivering it on worksheet/slides to them? What difference in the impact of the learning would it make? 







Should your child need an intensive program beyond just academics in this PSLE, you can check it out here! 




Cheers, 
Lisu 
ISUN Trainer

Comments

  1. Lash11 May 2021 at 02:32

    Thanks its really useful, my next step is to find best PSLE tuition

    ReplyDelete

Post a Comment

Popular posts from this blog

Answers to PSLE Questions

By
Why do I write suggested solutions to Red Swastika 2018 SA1 Paper? - My students found it useful and requested for more!  - The parents who used it to help their child have found it useful!  That's why despite using 4 hours just to write ONE SET of the suggested solutions (Section B only) and doing the miscellaneous admin such as scanning, downloading documents, writing email to send out to our ISUN warriors, I do it.  Hope that all these will contribute to their learning :)  From the paper, there are quite a couple of questions from the PSLE Booklet: You can download the Red Swastika 2018 Paper here!  Red Swastika 2018 Q 30 Reproduction of Plants PSLE 2018 Q15 TEST IT OUT!  PSLE 2018 Q15 ANSWER  Red Swastika 2018 Q33 Adaptations PSLE 2013/ Specimen Paper Adaptions TEST IT OUT!  PSLE 2013/ Specimen Paper Adaptions ANSWERS Refer to other posts to learn more! Water cycle: https://acepslescience.blogspot.com/20
13 comments
Read more

Respiration and Photosynthesis

By
Respiration and Photosynthesis With air quality going downhill, there may be chances that we need to carry plants around as our oxygen tank.  The working mechanism is based on 2 simple concepts of Primary 5 Science, Respiration and Photosynthesis.  As seen from the picture, the man is wearing a mask connected to the plant. As the man respires, it gives out carbon dioxide.  The carbon dioxide, together with water and light, the green plant with cholorphyll photosynthesises and produces oxygen for the man to respire and survive.   A summary of the both respiration and photosynthesis processes are below: Respiration Respiration is the breaking down of digested food with oxygen to produce energy. The equation of Respiration Sugar (from digested food) +  Oxygen (from inhaled air)   รจ  ENERGY (for body to use) +  Carbon Dioxide (to exhaled air) + Water Vapour (to exhaled air)  *NOTE* All living things respire including plants. Respiration takes place ALL the
5 comments
Read more

Amazing Animals' Adaptations 2: The Light of Death

By
From the land, let's move on to the pitch dark sea. In the dark, many water creatures seek out for the light. However, unbeknown to them, they are courting their own death. Let's take a closer look at this deep sea angler fish. You may find it familiar as you may have seen from the movie, Finding Nemo. Anglerfish Adaptations: Light-emitting structure - Structural adaptation to attract prey so as to catch it Waving light-emitting structure - Behavioural adaptation to attract prey so as to catch it Many sharp jagged-teeth that are angled inwards - Structural adaptation to catch hold of prey easily and preventing them from escaping   ¹   Extended jawline - Structural adaptation to swallow prey easily Expandable Stomach - Structural adaptation to feed on prey bigger than itself and stock up food in the food-scare dark waters  ¹ Special sense organ  - Structural adaptation to look for mate and reproduce Male anglerfish attach himself to female anglerfish: Behavi
1 comment
Read more