revision: Physics - Topic 1

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Mass is the amount of matter in a substance. Measured in kilograms or grams. To measure mass, you could use a top-pan balance. Mass does not change at all, no matter how great the distance from the center of the Earth the thing we are measuring is.

Weight is the amount of gravitational pull or attraction acting on an object. It is measured in newtons, which you can use a newton or force meter to measure. The weight of an object decreases and the distance from the center of the Earth increases.

Remember -> You can use a triangle to remember this. =Just remember the Korean show "We Got Married" AKA WGM, so you get 'W=GxM'
weight = gravitational pull x mass
mass = weight/gravitational pull
gravitational pull = weight/mass

NEWTON'S LAWS-
1. An object will continue at constant speed in a straight line or stay at rest if there is no resultant force.
2. Acceleration is proportional to force for a constant mass.
3. Every force has an equal or opposite force. [Action = Reaction]
             
        Reaction on floor
               ^
Thrust <-    -> Air resistance (fluid friction) <A fluid is anything you can pour.
               V
           Weight

Vocab-
accelerates
slows down/decelerate
constant speed/terminal velocity
stationary

EXPLANATION-
At the start, there is only one force on the sky-diver. This is his weight. This is an unbalanced or resultant force that causes him to accelerate as he falls. As he travels faster and his speed increases, the friction - air resistance - increases. Eventually, the two forces become equal and balanced with no resultant force. He stops accelerates and travels or falls at a constant speed or TERMINAL VELOCITY.
When he opens his parachute, the air resistance increases and the forces are no longer equal but there is a resultant force again, upwards. This makes him slow down until the two forces are equivalent again. And when the two are balanced with no resultant force, he one again travels at a constant speed. His new TERMINAL VELOCITY.
When he is near the ground, it pushes up to make him decelerate quickly. When he stands on the ground, the ground pushes up on his feet. That upward force (the reaction) is equal to his weight, so there is not resultant force and he is stationary.

[When the parachute opens, the surface area increases and so does the air resistance along with it causing his speed to decrease.]

Rain does not fall faster and faster and fall at terminal velocity because the weight of the raindrop and the air resistance is equivalent, which means there is no resulting force (no acceleration).

DENSITY, MASS and VOLUME.
density = mass/volume
density units -> g/cm^3 or kg/m^3

Remember -> DMV "The Music Video" :)

*To find the volume of different shapes, you have equations.* - Not needed.

SPEED, DISTANCE and TIME
distance = speed/time
USE THE TRIANGLE

Remember -> Don't Smoke Tobacco