Definitions 1 Flashcards
Homogenous equations
A homogeneous equation has both sides of the equation with the same base units, meaning the equation equals zero
Scalar
Physical quantities with a magnitude/size
Vector
Physical quantities with a magnitude/size and direction
Accuracy
How close a reading is to its true value
Precision
The smallest change in value that can be measured by an instrument
Random errors
Uncontrollable errors that change with each reading and are caused by unknown and unpredictable changes
Systematic errors
Errors caused by the imperfection of an instrument, causing readings to differ from the true value by a consistent
Uncertainty
The range of values within which a measurement is likely to be in
Acceleration
The rate of change of velocity
Displacement
The straight line distance between a start and finish point in a specific direction
Distance
The total length travelled by an object
Speed
The distance travelled per unit time
Terminal velocity
The maximum constant velocity of an object in free fall when the resultant force reaches zero
Velocity
The rate of change of displacement
Conservation of momentum
The total momentum of an isolated system remains constant when there are no external forces acting on the system
Elastic collisions
Collisions where:
- The total momentum AND kinetic energy of the system are conserved
- The relative speed of approach = the relative speed of separation: u1 - u2 = v2 - v1
Force
The rate of change of momentum
Inelastic collisions
Collisions where:
- ONLY the total momentum of the system is conserved
- The total kinetic energy is NOT conserved
Linear momentum
The product of mass and velocity
Mass
The measure of the amount of matter in an object, determining its resistance to acceleration
Newton’s 1st law
A body remains at rest or with constant velocity unless acted on by a resultant force
Newton’s 2nd law
The resultant force is proportional to the rate of change of momentum
Newton’s 3rd law
If one body exerts a force on another, it will experience an equal in magnitude, but opposite direction force by the other body
Weight
The downward force due to the gravitational field
Centre of gravity
The point at which the weight of an object may be considered to act
Density
The mass per unit volume of an object
Conditions for equilibrium
- There is no resultant force
- Sum of clockwise moments = sum of anticlockwise moments
Moment
The turning effect of a force
Pressure
The perpendicular force per unit area
Principle of moments
The sum of all clockwise moments about a point = the sum of all anti-clockwise moments about the same point
Couple
A pair of forces that act to produce rotation or torque
Energy
The ability to do work
Work done
The product of a force and the distance moved in the direction of the force
Gravitational potential energy
Energy stored due to the height or position of a mass in a gravitational field
Kinetic energy
Energy of an object due to its motion
Power
The work done or energy transferred per unit time
7 SI base quantities
- Mass - kg
- Length - m
- Time - sec
- Current - A
- Temperature - K
- Amount of a substance - mol
- Luminous intensity - cd
How does an object in free fall reach terminal velocity?
- The resultant force due to the weight of the object is initially much greater than the air resistance
- The object’s velocity increases as it continues to fall, which causes the drag force to increase
- The increase in drag force decreases the resultant force until it reaches zero
- When the drag force equals the weight of the object, terminal velocity has been reached
Hydrostatic pressure
The pressure exerted by a fluid on an object in equilibrium within the fluid due to the force of gravity
Atmospheric pressure
1.01 x 10^3 Pa
Archimedes’ law
When an object submerged in a fluid is at rest, it has an upward buoyancy force or upthrust equal to the weight of the fluid displaced by the object
Archimedes’ principle equation
F = p * g * V
F = upthrust force in N
p = density of fluid in kgm^-3
V = volume of fluid displaced in m^3
Upthrust
The resultant force acting on an object submerged in a fluid, which is due to the difference in hydrostatic pressure at the top and bottom of the object
How many significant figures should you write uncertainties to?
- Always give the uncertainty to the same sf as all the other uncertainties given
- For percentage uncertainties the uncertainty should be given to 2sf
Equation relating work to energy
Work = ∆E
W = ∆EK ∆GPE = ∆EP
What happens if all EK is transferred to GPE or EP?
- ∆EK = ∆GPE
- ∆EK = ∆EP
How do you calculate work done against resistive force?
W resistive = W - ∆EK
How do you calculate the total resistive forces acting on an object?
F net = mg - F resistive
F net = sum forces in the direction of motion - sum forces opposing the motion in the opposite direction of motion
How do you fix a systematic error?
- If there is a zero error, subtract it from all the readings
- Use a new or different instrument and retake the readings
How do you reduce the affect of a random error?
Take multiple readings and then find the average of the readings
Scalar quantites
Distance, speed, mass, time, energy, volume, density, pressure, electric charge, temperature
Vector quantities
Displacement, velocity, acceleration, force, momentum
Conditions of a couple
- The forces are equal in magnitude, but opposite in direction
- The forces must be perpendicular to the distance between them
- The forces cannot share the same line of action
- A couple produces a resultant force of zero and hence, the object does not accelerate
When do you know if an object will float or sink in a fluid?
How do you know if an object will float or sink in a fluid?
- An object will float if the upthrust > the weight of the fluid displaced - i.e. the object is less dense than the fluid
- An object will sink if the weight > the upthrust - i.e. the object is more dense than the fluid
State the characteristics of a velocity-time graph:
- Gradient of the line = acceleration
- Area below the line = displacement
- When the line goes below the positive y-axis, it means the object is moving in the opposite direction
State the characteristics of a displacement-time graph:
- Gradient of the line = velocity
- When the line crosses the time-axis, the object passes through the starting position
When should the 5 SUVAT equations be used?
They describe any object moving with a constant acceleration
State the 5 SUVAT equations:
- v = u + at
- s = ut + (1/2)at^2
- s = vt - (1/2)at^2
- s = (v + u)t / 2
- v^2 = u^2 + 2as
What things should be considered during projectile motion?
The equation relating force, momentum and time
F = ∆p / ∆t
Change in momentum
∆p = p(final) - p(initial) = m(∆v)
Conditions for Newton’s 3rd law
The force pair must be:
- The same type of force
- The same magnitude
- Opposite in direction
- Acting on different objects
What affects the magnitude of drag forces?
Drag forces increase with the speed of the object and decrease as the object slows down
Inertia
An object’s resistance to changes in its motion or state of rest
Stable objects
Stable objects have a lower center of gravity and wider base
Equation for the moment of a force
T = Fd
d = perpendicular distance to the force to the pivot
How do you calculate a couple?
T = Fd
F = one of the forces
d = perpendicular distance between the forces
Equation for density
ρ = m / V
ρ = density in kgm^-3
Equation for pressure
p = F / A
p = pressure in Pa or Nm^-2
Equation for hydrostatic pressure
∆p = ρg∆h
Derive the equation for hydrostatic pressure
- W = mg
- ρ = m / V → m = ρV → W = ρVg
- ρV = ρAh → W = ρAhg
- p = F / A → W / A → ρAhg / A
- ∆p = ρg∆h
