Evan's Space

Wonders of Physics


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How to mark 2 points (at a distance apart) at the same level? (water finds its own level)

The video below demonstrates that water will find its own level.

An olevel question requires this concept:


An apartment block receives water from a nearby reservoir. A pump is necessary to lift the water into a storage tank at the top of the building.
The gravitational field strength is 10 N / kg. How much energy does the pump supply to lift each kilogram of water into the tank?

Solutions: 100J

Water will always find its own level. Hence with or without the pump, the water level in the pipe in the building will be of the same level as the reservoir. Hence, the pump is only needed to pump water up a height of 10m only (instead of the 50m).

Energy, E = mgh = 1 kg x 10 N/kg x 10m = 100 J

Click here for the post on this questions


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Hand Boiler

Hand boiler toy is a demonstration of thermal transfer and how the 3 states of matter interact.

The coloured liquid inside is usually ethyl alcohol, which is a volatile liquid (i.e. a liquid with low boiling point). Similar to the alcohol swab you applied on hand during injection. Such liquid evaporates easily in room temperature or when heat is applied to it.

Thermal energy flows from a region of higher temperature to a region of lower temperature. When we hold the boiler in our hand, the thermal energy from our hand (body temp about 37oC) is transferred to the lower bulb of the boiler. The ethyl alcohol evaporates and also due to heated air above the liquid, the air expands and the pressure increases. The air pushes the liquid down, hence pushing the liquid up the shaft into the top bulb.

The bubbling of the liquid in the top bulb is not due to ‘boiling’ of the liquid. Rather, the gas in the lower bulb continues to expand and it goes to the top bulb, hence giving the illusion that the liquid is ‘boiling’.


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Direction of Frictional Force on Tyre or Wheel (updated)

For these type of questions, it is important to identify which tyre/wheel is connected/powered by the engine or the person.

On each tyre or wheel, there are actually two types of frictional force.

  1. Frictional force on wheel
  2. Frictional force on road/ground

Examples:

2007PP P1Q5 Answer: Option D
2004PP P1Q5Answer: Option D
2021PP P1Q7 Answer: Option C


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Oscillating or Vibrating Object in a Wave Motion

When an object is oscillating or vibrating in a wave motion, the speed of the object varies along the path.

In this video, there are 3 examples of vibrating object.

1) Mass vibrating vertically from a spring

2) Pendulum bob oscillating

3) A particle vibrating up and down on a transverse wave

In general, when the object is at the extreme ends of the oscillation or vibration, it is momentarily at rest. Hence its KE at these points is minimum or 0 J.

And in the middle that is where the object is travelling the fastest, hence the KE is the maximum.


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Determine the motion of the particles on transverse wave

Instead of imaging how the particles will move and guess their motion, there is a technique which can help you to determine that.

In addition, when particles are in phase, it means that both particles on the wave have the same velocity and same displacement. It means both have the same speed in the same direction and same distance and direction away from the rest position.

Particles that are out of phase means both are having the same speed but in opposite direction.

Refer to the video below to find out more.

Question 01: 2005/2008 PP P1 Q20/Q18

Answer: Option D

Question 02: 2018 PP P1 Q24

Answer: Option B


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Revision on Kinematics

Video 01: The various physical quantities in kinematics

Video 02: Acceleration

Video 03: Graphical Analysis of Motion (Displacement (distance)-Time Graph and Velocity (speed)-Time Graph)

Video 04: Describing the motion of the car – practice

Video 05: Free-fall, acceleration due to gravity

Video 06: Motion of 2 objects


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1st Electricity Experiment

Below is a simple electrical experiment to determine the resistance of the unknown resistor. Take some time to look through these series of video to have a better understanding on how to do the connection and taking readings from the instruments.

Unknown resistor

Refer to this blog post for better understanding of the experiment and some information on ohmic conductor.

https://evantoh23.wordpress.com/2017/09/14/finding-unknown-resistor-r/

Basic set up

If Connections of Ammeter/Voltmeter are swopped

Different types of connecting wires

Connecting Variable Resistor

How To Read An Ammeter

How to Read A Voltmeter


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Reading Vernier Caliper and Micrometer Screw Gauge

The precision of ruler or measuring tape is 0.1 cm.

The precision of vernier caliper is 0.01 cm

The precision of micrometer screw gauge is 0.01 mm

This video will show you how to use a actual vernier caliper.

This video will guide you in reading the vernier caliper.

vernier caliper

This video will show you how to use a actual micrometer screw gauge.

This video will guide you in reading the micrometer screw gauge.

micrometer screw guage


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Basic Concepts on DC Circuit – river system

The ‘D.C.’ here mean direct current. It means that the current flows in one direction in the circuit.

The direction of the direct current refers to the conventional current, and it flows out of the positive (+) terminal of the cell / battery, around the circuit and flows back into the negative (-) terminal.

[Note: the direction of the electron flow is opposite to the conventional current]

To understand DC circuit, it will be useful to relate to a river system. Refer to the 3 videos below to learn more about 01: DC circuit similar to river system, 02: Series Circuit 03: Parallel Circuit and 04: Combined Circuit.

01: How is DC circuit related to a river system

02: Series Circuit

03: Parallel Circuit

04: Combined Circuit (Series and Parallel)

Now, after you have the basic concepts and rules for the circuits, let’s look at some simple example to reinforce you understanding.

Example 01: Series Circuit

Example 02: Parallel Circuit

Example 03: Combined Circuit

Example 04: PP2012P2Q7 DC circuit : pd across 2 points on two separate branches.

Hope these series of videos help in you understanding of DC circuit.


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Slinky Coil – Interesting Tricks and demonstrations of Transverse and Longitudinal Waves

Slink coil is usually used to demonstrate the two types of waves – transverse and longitudinal waves. But remember that when you are asked to state an example of each wave, do not quote slinky coil.

View the videos below to know more about the two types of waves.


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Pins inside and outside of beaker filled with water – 2012 sciphy practical

A pin in the beaker of water appears higher than its actual position due to refraction of light.

In this experiment, you have to adjust the pin at the cork to a suitable height, such that the pin and the image of the pin inside the beaker of water is aligned and that ‘pins at position of no parallax’ position.

The video below guides you in adjusting the height of the pins to locate correct height.

Similar kind of experiment: Pins with Lens and mirror

Other types of experiments involving pins.


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Light Experiments – Glass Block and Pins

The video include 3 different light experiments which involve glass block and pins.

Most students faced difficulties in locating the pins through the glass block. It is important to close one eye and use your master eye to view.

Hope this video helps!

In experiments like this, the sources of error include:

– the holes created by the pins are too big, hence the line drawn using the two holes may not be very precise, hence affecting the distance/angle measured (depends on experiments)

– When putting back the glass block back on the paper, the position may be not exactly the same, hence affecting the angle/distance measured.

As a precaution, it is good to ensure that the distance between the two pins are more than 4 – 5 cm. With the holes further apart, the line drawn will be more accurate.


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Fiery Re-entry into Earth’s Atmosphere (updated)

This post was updated following the first astronauts launched by SpaceX returned home safely on 3 Aug 2020.

SpaceX’s Crew Dragon heat shield shown off after first orbital-velocity reentry

How do spacecraft re-enter the Earth? | HowStuffWorks

Why Is It So Difficult For A Returning Spacecraft To Re-Enter Our Atmosphere?

Returning from Space: Re-entry – PDF format

SpaceX In-Flight Abort Test

SpaceX Falcon Heavy- Elon Musk’s Engineering Masterpiece

Shuttle Atlantis STS-132 – Amazing Shuttle Launch Experience

How to Land the Space Shuttle… from Space

First astronauts launched by SpaceX return to earth (3 Aug 2020)