Speed, Density, Pressure And PMoM Flashcards
What speed is walking?
1.5 m/s
What speed is running?
3 m/s
What speed is biking?
6 m/s
What factors affect the speed you travel at?
Age
Terrain
Fitness
What speed is driving?
25 m/s
What does a diagonal upwards line mean on a distance time graph?
Travelling at a constant speed
What does a horizontal line mean on a distance time graph?
Object is stationary
What does a steeper diagonal upwards line mean on a distance time graph?
Travelling faster, but still at a constant speed
What does a curved upwards line mean on a distance time graph?
Object is accelerating
What does a plateauing line mean on a distance time graph?
Decelerating
What does a diagonal downwards line mean on a distance time graph?
Constant speed in the opposite direction, towards start point
What does the gradient of a distance time graph show?
The speed of the object
Difference between determining average speed and instantaneous speed on a distance time graph?
Average speed is just total distance/total time, but fir instantaneous speed, draw a tangent and use the tangent triangle to do distance/time
Define acceleration
Rate of change of velocity
What is the symbol for acceleration and how is it measured?
a
m/s²
Equation for acceleration?
△v
a = —-
t
What does a velocity time graph show?
How an objects velocity changes with time
What does a diagonal upwards line mean on a velocity time graph?
Accelerating at a constant rate
What does a horizontal line mean on a velocity time graph?
Constant velocity
What does a curved upwards line mean on a velocity time graph?
Accelerating at an accelerating rate
What does a diagonal downwards line mean on a velocity time graph?
Constant deceleration
What does the gradient show on a velocity time graph?
An objects acceleration
What does area under a velocity time graph show?
Distance travelled
Symbol for density and what is it measured in?
ρ (rho)
Kg/m³
Symbol for volume and what is it measured in?
V
m³
Equation for density?
m
ρ = —-
V
What is 1m³ in cm³?
1,000,000 cm³
(You must convert for every dimesion)
How to work out density of an irregular object?
Place object into displacement can, volume of water displaced is equal to volume of object
(Archimedes principle)
Then continue as normal
How to work out density for a liquid?
Measure volume with a measuring cylinder, and weigh on a mass balance (making sure to zero it after placing empty measuring cylinder on)
Then carry on as normal
What is the symbol for area and what is it measured in?
A
m²
What is the symbol for pressure and what is it measured in?
p
N/m² or pascals, Pa
(1 Pa = 1 N/m²)
What is a scalar measure?
Magnitude only
What is a vector measure?
Direction and magnitude
Is mass vector or scalar?
Scalar
Is weight vector or scalar?
Vector
Is force vector or scalar?
Vector
What is distance?
How far an object moves (no direction), so is a scalar quantity
What is displacement?
Straight line from start to finish, involves direction, so is vector
What is resultant force?
The net force acting on an object
Eg. 2N to right, 4N to left, so Fres is 4N to left
How is resultant force worked on 2 planes?
With pythagoras and trigonometry
What does Newton’s first law state?
If resultant force on an object is 0,
If stationary, it will remain stationary
If moving, it’ll stay moving the same direction at same speed
How to work out which equation to use for acceleration and velocity?
Use suvat
S = distance
u = initial velocity
V = final velocity
a = acceleration
t = time
Work out what you are missing, not what you’re trying to work out
If missing s, distance, use
V-u
a= —–
t
If missing t, time, use
V² = u² + 2as
What is the difference between random and systematic errors?
Random errors can make the experiment wrong in any way eg. Temp fluctuations
Systematic errors make the experiment wrong the same way each time eg. Low res. Ruler
How to calculate uncertainty?
Range x ½
What does Newton’s second law state?
The acceleration of an object is proportional to the resultant force acting on an object, and inversely proportional to the mass of it
What is the equation of newtons second law?
F = ma
How to describe falling and terminal velocity
Frav
Forces acting
Resultant force, inc. direction
Acceleration, inc. direction
Change in velocity
Then repeat for force changes
What does Newton’s third law state?
When two objects interact, the forces they exert on each other are opposite and equal.
Eg propellor of boat pushes boat forwards and water back, birds winds push bird upwards and air downwards
What is stopping distance?
Distance travelled between seeing obstruction and halting
What is thinking distance?
How far car travels during reaction time
What is braking distance?
Distance travelled between brakes pressed and car halting
Equation for stopping distance?
Stopping distance = thinking distance + braking distance
Equation for thinking distance?
Thinking distance = speed x reaction time
Factors that can affect thinking distance
Reaction time
Drugs/alcohol
Tiredness
Age
Distractions
Speed
Factors that can affect braking distance
Weather/road condition (ice on road means less friction)
Mass of vehicle
Tyre condition (friction)
Brake condition (friction)
Speed
Properties of a solid?
Fixed regular arrangement
Low energy
Vibrate around a fixed point
Properties of a liquid?
- close together, irregular arrangement
- more energy, move in random directions at low speed
- can move past each other
Properties of a gas?
- far apart, almost no forces of attraction between particles
- high energy
- free to move, travel in random directions at range of speeds
Which states are fluids?
Gas and liquids
Which states can compress?
Only gas
How is atmospheric pressure created?
Air molecules colliding with a surface
How do you explain pressure in a fluid?
- particles in a fluid are moving, collide with surfaces, exerting a force and therefore a pressure, because p=F/A. Pressure is exerted normal to the surface, no matter the direction of the particle
How thick is the atmosphere?
100km
Explanation for lower atmospheric pressure at higher altitudes?
Less dense atmosphere, fewer air molecules to collide with surface, lowering pressure
Or
Higher altitude means fewer air molecules above a surface, meaning less weight pushing on surface, so less pressure
What is the internal energy of a system?
The total energy that its particles have in their kinetic and potential stores
What is temeperature a measure of?
The average kinetic energy of particles in an object
How does decreasing a sealed container’s volume affect pressure?
- Decreasing volume
- More FREQUENT collisions
- Greater force exerted on surface
- Increased pressure
How does increasing the temperature of a sealed container affect pressure?
- Increased temp.
- Increases avg. kinetic energy of particles
- More FREQUENT and higher force collisions
- Greater total force exerted on surface
- Increased pressure
What is boyle’s law?
A constant for a fixed mass if gas held at a constant temperature, so pressure is inversely proportional to volume
Equation for Boyle’s law?
pV = constant
What is Pascal’s vase?
A vase with different shaped columns, when filled with water, the surface is still at a constant level
Why is pressure greater deeper in a fluid?
There is a greater weight of fluid pushing down on you
Equation for pressure in liquid?
p = hρg
(Depth x density of liquid x gravitational field strength)
What is upthrust?
Where the force exerted on bottom surface is greater than the force acting on the top surface of an object, causing a resultant upwards force and therefore it floats
What happens when an object less dense is placed in a denser fluid?
It floats to the surface until it displaces a volume of fluid equal to its weight
What happens when a denser object is placed in a less dense fluid
It sinks, as it cannot displace enough fluid equivalent to its weight
What happens during a change of state?
Temperature of substance remains constant, until it changes state
Heating during this period increases potential energy and weakens bonds, but doesn’t increase kinetic energy
What happens when you heat a substance while not changing state?
Increases both KE and PE of particles, so temperature rises
What is the energy required to change a substances state called?
Latent heat
What is specific latent heat?
The energy needed to change 1kg of a substance from one state to another eithout changing temperature
What is the specific latent heat of fusion of water?
340,000 J/kg
What is the specific latent heat of vaporisation of water?
2,260,000 J/kg
Why does vaporisation require more energy than fusion?
Because fusion is just weakening/strengthening bonds, whereas vaporisation is breaking bonds or forming them
What is the symbol for specific latent heat and its units?
L
Joules per kilogram, (J/kg)
What changes of state are fusion?
Melting and freezing
What changes of state are vaporisation?
Boiling and condensation
Which changes of state require energy, and which release energy?
Melting and boiling require energy
Freezing and condensation release energy
What is the equation that shows the relationship of specific latent heat?
E = mL
What is specific heat capacity?
The energy needed to raise the temperature of a 1kg of a substance by 1°c
What is the symbol for specific heat capacity and its units?
c
J/kg°c
What is the symbol for temperature and its units?
θ
°c
What equation shows the relationship of specific heat capacity?
△E = mc△θ
What is the specific heat capacity of water?
4200 J/kg°c
How to combine specific and latent heat
Draw a diagram of temp against time
Count the sections, and do calculations for each
Why does pumping air into a mattress cause it to inflate, in terms of pressure?
- air pumped in
- more air particles in mattress
- more frequent collisions, so more force exerted and greater pressure
- as pressure becomes greater than atmospheric pressure, mattress expands so pressure inside remains at atmospheric pressure
Why does a mattress feel warm as it is pumped up?
Work is done, transferring energy to kinetic stores of air particles, increasing temp
