Chapters 1 - 8 Flashcards
What is accuracy
Close to the common or true value
Define precision
How close the spread of data is
What is a systematic error
It happens with a consistent error in apparatus, reduced by using better equipment
Zero Error
When the equipment shows an initial value of 0
Parallax Error
Produced when the scale / gauge is read incorrect
Random Error
Caused by unknown changes to the apparatus or conditions
Percentage uncertainty
(uncertainty/average value)x 100
Vector
Quantity with direction and magnitude
Scalar
Quantity with only magnitude
Resolving Vectors ( x and y direction )
Fx = F x cos theta Fy = F x sin theta
Normal Contact Force Equations
mg cos theta = perpendicular to slope
mg sin theta =parallel to slope
Moment of a Force
Force x perpendicular distance
Principle of moments
Sum of clockwise moments = sum of anticlockwise moments
Net force = 0
Couples
Pair of equal and opposite forces acting on a body, not in same direction
Torque
The moment of a couple
One of forces x Perpendicular distance between forces
Archimedes Principle
Upthrust exerted on a body immersed in a fluid is equal to the weight of the fluid displaced by the body
Principle of conservation of energy
Total energy of a closed system remains constant, energy cannot be created or destoyed.
Hookes Law
Extension is directly proportional to force applied, until elastic limit is exceeded.
Force applied = Force constant x extension
Area under force - extension graph
Work done
Work done equation
Force x Distance
Elastic Potential Energy
1/2 x force x extension.
or
1/2 x force constant x entension^2
Tensile Stress
Force / Cross Sectional Area
Tensile strain
Extension / original length
Young Modulus
Tensile stress / tensile strain
FL / Ax
Malleable Material
Can be formed into sheets
Ductile Material
Can be easily shaped, into wires
Strong Material
High ultimate tensile strength
Yield Point
The point on a stress - strain graph beyond which the deformation is no longer entirely elastic.
Breaking strength equation
Breaking force / cross sectional area
Newtons First Law
An object will stay at rest or continue at constant speed unless an external force acts on it
Newtons Second Law
The rate of change of the object is proportional to the force acting on it.
Newtons Third Law
For every action force there is an equal and opposite reaction force on another body.
Conservation of momentum
For a system of interacting objects, the total momentum remains constant as long as no external forces act on the system
Linear Momentum equation
mass x velocity
Compare momentum and energy in elastic and inelastic collisions.
In both cases momentum and energy are conserved.
For inelastic collisions kinetic energy is not conserved.
Impulse of a force
Force x change in time.
A resultant force causes the object to accelerate.
Electric Current
The rate of flow of charge. Amperes (A)
Net Charge equation
Q = +- ne e = 1.6 x 10 ^-19
Convectional Current
It flows from the positive to negative side.
Electron Flow
It flows from the negative to positive side.
Structure of a metal
Regular crystal structure lattice of + ions
Surrounded by a number of free / delocalised electrons
Positive ions vibrate around a fixed point
Electrolytes
Liquids that can carry electric current
What are anions
Positively charged ions
What are cations
Negatively charged ions
Mean Drift Velocity
The higher the number density, the greater the number of free electrons , the better the conductor.
I = anev
What is the effect of increasing the cross sectional area of a wire on mean drift velocity
The wider the wire, the lower the drift velocity, current stays the same.
If current increases, mean drift velocity ……
Increases, the electrons move faster
If the wire is thinner, electrons move….
Faster, same force so electrons move quicker
If number density is small, mean drift velocity is
Large, less likely to collide and slow down.
Why cant insulators conduct a charge
They don’t have enough free electrons to carry a charge
