| Mass | Weight |
|---|---|
| A measurement of the amount of substance in a body. | A measurement of the amount of gravitational force acting on a body |
| SI Unit: kilogram (kg) | SI Unit: newton (N) |
| Constant regardless of the gravitational field strength | Varies according to the gravitational field strength |
| Measured by a beam balance or electronic balance | Measured by a spring balance |
| Scalar quantity | Vector quantity |
Category: Pure Physics
What is a scalar quantity? Give some examples.
It is a physical quantity with only numerical magnitude.
Examples: mass, energy, time, volume, density, power, temperature, speed.
What is a vector quantity? Give some examples.
It is a physical quantity with both numerical magnitude and direction.
Examples: force, velocity, acceleration, weight, displacement.
What is a physical quantity?
A physical quantity is a quantity that can be measured.
It consists of a numerical magnitude and a measurement unit.
Eg, length, area, volume, velocity, acceleration
What is Brownian Motion? What causes Brownian Motion?
Brownian motion refers to the constant, random motion of small suspended particles in a fluid.
Brownian motion is caused by the constant, random bombardment of the fluid particles on the small suspended particles from all directions, causing the small suspended particles to move constantly in a haphazard motion.
Describe how a barometer work.
A barometer consist of a long glass tube and a liquid reservoir, usually mecury.
The tube is first submerged in the reservoir, and completely filled with the liquid in the reservoir.
Then, the tube is held inverted to a vertical position, with the mouth of the tube still in the liquid reservoir, and a pocket of vacuum above the liquid column inside the tube.
The atmospheric pressure exerts a force on the surface of the liquid reservoir, pushing the liquid up the tube. The pressure of the liquid column in the tube will be equal to the atmospheric pressure.
Describe how a hydraulic press work.
A hydraulic press consists of two pistons of different sizes.
The space between the two pistons is filled completely with a liquid, usually hydraulic oil.
When a force is applied on the smaller piston, the pressure exerted on the liquid at the smaller piston is transmitted equally throughout the liquid.
Hence, the same pressure is also exerted at the bigger piston.
Since P = F/A, the F/A ratio will be the same at both pistons.
Since A1 < A2, hence F1 < F2.
So a smaller effort on the smaller piston (F1) will be able to lift a bigger load at the bigger piston (F2).
Double-Pivot Push-up
Describe the effects of absorbing electromagnetic waves.
Heating Effect
– Infrared heating
Fires and hot bodies emit infra-red radiation. Our skin absorbs the infra-red rays, making us feel warm.
– Microwaves heating
Microwaves are of a non-ionizing character. However, microwaves, being more penetrative, can cause more severe burns to the skin, especially when skin has high water content.
Ionisation Effect
UV rays, X-ray, Gamma ray can cause breakdown of DNA, and ionization of molecules and atoms in living matter. The mutation of these cells and atoms can lead to formation of cancerous cells.
Describe in terms of the arrangement and movement of particles, the process of ice melting.
When ice melts, the heat energy gained from surroundings is used to weaken the bonds between particles. The movement of the particles changes from vibrating in fixed positions in the solid state to moving and sliding over one another freely in confined spaces in the liquid state. The arrangement of the particles changes from regularly arranged, tightly packed together in the solid state to irregularly arranged, close together in the liquid state.
The average kinetic energy of the particles remains constant, so temperature remains constant during melting.