BLOCK 1: GENERAL PHYSICS LUCIA ROMERO
1.1 LENGTH AND TIME
To find a length
How do you measure the thickness of a sheet of paper?
• When measuring distances of a few cm → ruler
1. Place 100 sheets of paper between the claws
• When measuring larger distances (of a few meters) → tape measure
2. Turn the ratchet until a click is heard, then remove the paper
• When measuring even larger distances → trundle wheel
3. Read the vertical and horizontal scales
• When measuring very small distances → micrometer screw gauge
4. Divide by 100
How can we avoid parallax when measuring lengths?
1. By looking at the ruler perpendicularly
2. Making sure the measurement starts at 0cm
To find volume
• When measuring the volume of liquids → measuring cylinder
How do we measure from a measuring cylinder?
By looking at the bottom of the meniscus, except for mercury, where you measure from the top
To find time
• When measuring time intervals → stop-clock or stopwatch
How do we measure short, repeated, time intervals?
→ By first timing the number of cycles, and then, dividing by the total number of cycles
1. Start the stopwatch at a specific point in the cycle
2. Measure 10 cycles
3. Divide by 10
4. Obtain an average of 1 oscillation
→ so:
𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑦𝑐𝑙𝑒𝑠
e.g., piston, period of a pendulum
, BLOCK 1: GENERAL PHYSICS LUCIA ROMERO
1.2. MOTION
DEFINITIONS:
1. Speed (measured in m/s): the distance moved by an object each second
2. Velocity: speed in a specified direction
3. Acceleration: the rate of change of velocity (how much the velocity of an object changes by every second)
FORCES
When a force acts on an object, it can do 3 things:
1. Change in direction
2. Change its speed
3. Change its shape
When the forces on an object are equal the object → will either: 1. Not move
2. Move at a constant speed
Unbalanced forces → cause acceleration
CALCULATING AVERAGE SPEED
𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑 =
𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒
VELOCITY
How is it different to speed?
It includes a direction (the direction of travel) as well as its value (its magnitude)
ACCELERATION
How do we calculate it?
𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛
(𝑣−𝑢)
SO, 𝑎 = (where u is the initial velocity and v is the final velocity)
𝑡
• The units of acceleration are m/s2, which mean the same thing as m/s/s – the change in velocity (in m/s) every second
DISTANCE – TI ME GRAPHS
• They show how the distance of an object (from a point) varies over time
What do different lines mean in these graphs?
1. A horizontal line → stationary
2. A straight line → constant speed
3. If the gradient increases → the object is speeding up (accelerating)
4. If the gradient decreases → the object is slowing down (decelerating)
5. If the line is going down → the object is moving backwards
Calculating speed
The speed of an object is given by the gradient of the line
𝑟𝑖𝑠𝑒
𝑠𝑝𝑒𝑒𝑑 = 𝑔𝑟𝑎𝑑𝑖𝑒𝑛𝑡 =
𝑟𝑢𝑛
VELOCITY/SPEED – TIME GRAPHS
A Velocity-time graph shows how the velocity (or speed) of an object changes over time
What do different lines mean in these graphs?
1. If the line is horizontal → the velocity is constant (no acceleration)
2. If the line slopes upwards→ the object is accelerating (speeding up)
3. If the line goes down →the object is decelerating (slowing down)
1.1 LENGTH AND TIME
To find a length
How do you measure the thickness of a sheet of paper?
• When measuring distances of a few cm → ruler
1. Place 100 sheets of paper between the claws
• When measuring larger distances (of a few meters) → tape measure
2. Turn the ratchet until a click is heard, then remove the paper
• When measuring even larger distances → trundle wheel
3. Read the vertical and horizontal scales
• When measuring very small distances → micrometer screw gauge
4. Divide by 100
How can we avoid parallax when measuring lengths?
1. By looking at the ruler perpendicularly
2. Making sure the measurement starts at 0cm
To find volume
• When measuring the volume of liquids → measuring cylinder
How do we measure from a measuring cylinder?
By looking at the bottom of the meniscus, except for mercury, where you measure from the top
To find time
• When measuring time intervals → stop-clock or stopwatch
How do we measure short, repeated, time intervals?
→ By first timing the number of cycles, and then, dividing by the total number of cycles
1. Start the stopwatch at a specific point in the cycle
2. Measure 10 cycles
3. Divide by 10
4. Obtain an average of 1 oscillation
→ so:
𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑦𝑐𝑙𝑒𝑠
e.g., piston, period of a pendulum
, BLOCK 1: GENERAL PHYSICS LUCIA ROMERO
1.2. MOTION
DEFINITIONS:
1. Speed (measured in m/s): the distance moved by an object each second
2. Velocity: speed in a specified direction
3. Acceleration: the rate of change of velocity (how much the velocity of an object changes by every second)
FORCES
When a force acts on an object, it can do 3 things:
1. Change in direction
2. Change its speed
3. Change its shape
When the forces on an object are equal the object → will either: 1. Not move
2. Move at a constant speed
Unbalanced forces → cause acceleration
CALCULATING AVERAGE SPEED
𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑 =
𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒
VELOCITY
How is it different to speed?
It includes a direction (the direction of travel) as well as its value (its magnitude)
ACCELERATION
How do we calculate it?
𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛
(𝑣−𝑢)
SO, 𝑎 = (where u is the initial velocity and v is the final velocity)
𝑡
• The units of acceleration are m/s2, which mean the same thing as m/s/s – the change in velocity (in m/s) every second
DISTANCE – TI ME GRAPHS
• They show how the distance of an object (from a point) varies over time
What do different lines mean in these graphs?
1. A horizontal line → stationary
2. A straight line → constant speed
3. If the gradient increases → the object is speeding up (accelerating)
4. If the gradient decreases → the object is slowing down (decelerating)
5. If the line is going down → the object is moving backwards
Calculating speed
The speed of an object is given by the gradient of the line
𝑟𝑖𝑠𝑒
𝑠𝑝𝑒𝑒𝑑 = 𝑔𝑟𝑎𝑑𝑖𝑒𝑛𝑡 =
𝑟𝑢𝑛
VELOCITY/SPEED – TIME GRAPHS
A Velocity-time graph shows how the velocity (or speed) of an object changes over time
What do different lines mean in these graphs?
1. If the line is horizontal → the velocity is constant (no acceleration)
2. If the line slopes upwards→ the object is accelerating (speeding up)
3. If the line goes down →the object is decelerating (slowing down)
