Density and Pressure Flashcards
Density symbol
rho (ρ)
Density formula
Density = mass/volume
ρ = mass/volume
Pressure formula
Pressure = Force perpendicular to the area/Area
p =F/A
% difference formula
% Difference = accepted value −calculated value/accepted value × 100
Pressure at depth of fluid
p = hρg
What there must be for an of an object floating?
For equilibrium, force upward = weight downward
How to calculate the upthrust of an object
Upthrust = Weight of object or U = mg
How to calculate the forces acting on an object from all sides
Ftop = Ahρg and
Fbottom = A(h + x)ρg
Fres = U = A(h + x)ρg- Ahρg = Axρg
Archimedes’ principle
The weight of the fluid displaced by the object is equal to the upthrust of the liquid on the object.
What happens when work is done
Work is done when a force moves its point of
application.
Work done equation
work = force x distance moved in the direction of the force
Is work scalar or vector
A scalar quantity
If the direction of the force and the distance moved are
not in the same direction how do you find W?
W = F x cos θ
How to find work done on force distance graphs?
The area under the curve is equal to the work done.
Why is energy needed?
Energy is needed to move objects, to change their
shape or to warm them up.
Conservation of energy
The principle of the conservation of energy states that energy cannot be created or destroyed. Energy can change from one form to another.
Kinetic energy (KE)
Energy due to a body’s motion.
Potential energy (PE)
Energy due to a body’s position
Potential energy (PE)
Energy due to a body’s position
Thermal energy
Energy due to a body’s temperature.
Chemical energy
Energy associated with chemical
reactions.
Nuclear energy
Energy associated with nuclear
reactions.
Electrical energy
Energy associated with electric
charges.
Elastic energy
Energy stored in an object when it is
stretched or compressed.
Kinetic energy equation
kinetic energy = 1⁄2 x mass x (speed)2
EK = 1⁄2 m v2
Gravitational potential energy equation
change in g.p.e. = mass x gravitational field strength
x change in height
ΔEP = m g Δh
What happens to the GPE and KE when there is no resistance
If there is no significant air resistance then the initial gravitational energy of an object is transferred into kinetic energy.
Power def
Power is the rate of transfer of energy.
Power equation
power = energy transfer/time
P = ΔE/Δt
What happens when you combine the power and work equation
power = force x velocity
P = F v
What is energy efficiency
Energy efficiency is a measure of how usefully energy is used by a device.
Energy efficiency equation
efficiency = useful energy transferred by the device/total energy supplied to the device
Maximum efficiency number
1.0
Efficiency with power and energy equations
efficiency = useful work output/energy supplied
efficiency = useful power output /power input
Percentage efficiency equation
percentage efficiency = efficiency x 100
