Physics P1 - P4 Flashcards
Specific Heat Capacity
Change in thermal energy (J) = mass (kg) x specific heat capacity (J/kgC) x Change in temperature (C)
This is the energy needed to raised the temperature of 1kg of a substance by 1*C
Specific Latent Heat
Specific Latent Heat is the energy needed to change state
thermal energy for a change in state (K) = mass (kg) x specific latent heat (J/Kg)
Pressure of Gases
Changing the temperature changes the pressure - Directly proportional
Pressure(Pa) x volume (m^3) = constant
This is for a fixed amount of gas at a constant temperature
A change in pressure can also cause a change in volume - If the pressure of the gas increases then so does the force, sometimes causing the container to change volume
Liquid Pressure
Liquid Pressure causes upthrust and makes things float
If you submerge an object in a liquid, it experiences liquid pressure from all directions due to the particles of the liquid
Pressure = height of column x density of liquid x gravitational field strength (typically 10N/kg)
If the object is denser than the liquid then it will sink; the forces acting upon it will be greater than waters pressure that pushes it up
Speed, Velocity and Acceleration
Speed is a scalar quantity, whereas velocity is a vector quantity (it shows magnitude)
Acceleration is the rate of change of velocity
speed = distance / time
Acceleration = change in velocity / time
(final velocity)^2 - (initial velocity)^2 = 2 x acceleration x distance
Reading Velocity-Time Graphs
The acceleration on a velocity-time graph is the gradient
The total area under the graph is the distance travelled
Forces and Free Body Force Diagrams
Forces can be contact or non-contact. To exert a contact force, two objects must be touching, for example pushing or pulling an object. Friction is a contact force.
Non-contact forces are forces between two objects that aren’t touching. Electrostatic, magnetic and gravitational forces are all examples of this.
Resultant force is the overall force on a point or object, If the forces act upon the same line the resultant force is found by just adding or subtracting. If the resultant force is zero then all forces are balanced and nothing happens. If the resultant force is not zero, then the forces are unbalanced and motion will be made in that direction.
Scale drawings can also be used to find resultant force.
An object is in equilibrium if the forces on it are balanced
Netwon’s First Law of motion
An object will remain stationary or at constant velocity unless acted upon by an external force
In other words, no resultant force means no change in velocity
Newton’s Second Law of Motion
The force acting on an object is equal to its rate of change of momentum
f = ma
force (N) = mass (kg) x acceleration (m/s^2)
This force is always the resultant force
Inertia and Netwon’s Third Law of Motion
For every reaction there’s an equal and opposite reaction
Inertia is a measure of how difficult it is to change an object’s velocity. It is dependent on the inertial mass, which is force/acceleration. A larger inertial mass requires a larger force to accelerate by a certain amount
Momentum
Momentum (kg m/s) = mass x velocity (m/s)
p = mv
Force = change in momentum/time F = P/t
In a collision when no other external forces act, momentum is conserved - Total momentum after collision = total momentum before
Mass, weight and gravity
gravitational force (N) = mass (kg) x gravitation field strength (N/kg)
Investigating Hooke’s Law
You can investigate the extension of a spring with a practical, where you periodically add masses to a hook, stretching out the spring. Measure the extension and plot a graph of force (weight) against extension. After drawing a light of best fit, the gradient will be the spring constant.
energy transferred in stretching (J) = 0.5 x spring constant (N/m) x (extension)^2 (m)^2
E = 0.5 k x^2
The elastic limit is the point at which the spring starts to deform
Moments
A moment is the turning effect of a force. If a force acts on an object with a pivot, it can cause the object to rotate around the pivot. This size o the moment of the force is given by:
moment of a force (Nm) = force (N) x distance (m)
The distance here is the normal (perpendicular) distance between the pivot and the line of action.
Total anticlockwise moment = total clockwise moments
Levers and Gears
Levers act as force multipliers
Levers transfer the turning effect of a force - push one end of a lever down and the rotation around the pivot causes the other end to rise. Levers increase the distance from the pivot that the force is applied, so less input force is needed to get the same moment. This moment provides an output force to a load
The moment of the input force equals the moment of the output force. Moment = force x distance, which means you can write:
input force/output force = distance of output force from pivot/distance of input force from pivot
Gears fit together to transfer turning effects. A force applied to a small gear creates a small moment. The small gear applies this force to the gear next to it. if this gear is larger, the force is being applied from further from the pivot, so the moment of the second gear is larger. This multiplies multiple times.
