Basic Physics, Kinematics, Dynamics, Energy Concepts Flashcards
[def] Quantity
In SI: a number x a unit
[def] Scalar
Quantity with magnitude only
[def] Vector
Quantity with magnitude and direction
[def] Resolving a vector into components in particular directions
find vectors (components) in these directions, which vectorially add to make the original vector. Components are equivalent to original vector
[def] Density of a material (ρ)
Density = Mass/Volume
UNIT: kg m−3 or g cm-3
In which mass and volume apply to any sample of the material.
[def] Moment of a force
Moment of a force about a point is the force x the perpendicular distance from the point to the pivot
moment = F x d
UNIT: N m [unit is NOT J]
[def] Principle of moments
For a system to be in equilibrium, sum of total anticlockwise moments about a point = sum of total clockwise moments about the same point
[def] Center of gravity
the single point within a body at which the entire WEIGHT of the body may be considered to act.
Random errors
Reduced by repeat readings because they are out of your control
Systematic errors
reduced by calibrating the equipment because they are from the measuring equipment (or operator)
How to lay out uncertainty
quantity x ± u (then units here)
Uncertainty: how much?
Instrument resolution (when one reading)
or
Half the range (when spread of readings)
LARGEST ONE
How to reduce uncertainty (x2)
Larger quantity (or divide down) More precise instrument
percentage uncertainty calculation
(estimated uncertainty) / (mean value) X 100 %
uncertainty: multiply or divide quantity
add %u
uncertainty: multiplied by constant
SAME, UNCHANGED %u
uncertainty: raise quantity to power
%u multiplied by same power
uncertainty: add or subtract quantity
Add absolute u
SI units
kg, m, s, A, mol, K
two things to for a system to be in equilibrium
no net moment
no resultant force
[def] Displacement
Displacement of point B from point A is the shortest distance from A to B, together with the direction
UNIT: m
[def] mean speed
mean speed = (total distance traveled) / (total time taken)
= (delta x) / (delta t)
UNIT: m s-1
[def] Instantaneous speed
Rate of chance of distance
UNIT: m s-1
[def] mean velocity
mean velocity = (total displacement) / (total time taken)
UNIT: m s-1
[def] instantaneous velocity
rate of change of displacement
UNIT: m s-1
[def] mean acceleration
mean acceleration = (change in velocity) / (time taken)
= (delta v)/ (delta t)
UNIT: m s-2
[def] instantaneous acceleration
Rate of change of velocity
UNIT m s-2
[def] terminal velocity
the terminal velocity is the CONSTANT, MAXIMUM velocity of an object
when resistive forces on it are equal and opposite to the ‘accelerating’ force (ie the pull of gravity)
[def] Force, F
A force on a body is a push or a bull acting on the body from some external body
UNIT: N
Newton’s First Law
If an object experiences no resultant force, then its velocity is constant
Newton’s Third Law
If body A exerts a force on body B, then body B will exert a force on body A that is EQUAL IN MAGNITUDE and OPPOSITE IN DIRECTION
N3L pairs = same types of force (gravitational, contact, frictional, magnetic)
Newtons’s second Law (more ‘complex’ definition)
The rate of change of momenta of an object is proportional to the resultant force acting on it, and takes place in the direction of that force.
Newton’s second law (‘easier’ definition)
(sum of F) = m a
Mass of a body x its acceleration is equal to the vector sum of the forces acting on the body
This vector sum is called the resultant force
s-t graph:
Grad?
Area?
grad = acceleration
area under= distance
v-t graph:
Grad?
+ve grad = forwards motion
-ve grad = backwards motion
d-t graph:
Grad?
Line shape?
grad = velocity
curved line = accelerating
SUVAT
v = u +at s= vt - ½a(t^2) s= ut + ½a(t^2) s= ½(v+u)t (v^2)= (u^2) +2as
Projectile motion: how?
Split into horizontal and vertical components
Time will be same
Horizontal = s=vt
Vertical= SUVAT
Projectile motion: Horizontal and vertical - why?
SUVAT vertical because constant acceleration due to gravity
s=vt horizontal because we can ignore air resistance
PERPENDICULAR COMPONENTS ARE INDEPENDENT OF EACH OTHER
[def] Momentum
The momentum of an object is its mass multiplied by its velocity (p = m v).
Momentum is a vector.
UNIT: kg m s-1 or N s
[def] Principle of conservation of momentum
The vector sum of the momenta of bodies in a system stays constant (even if forces act BETWEEN the bodies)
Provided there is NO EXTERNAL resultant force.
[def] Elastic collision
Collision when there is NO CHANGE in total KE
[def] Inelastic collision
Collision when KE is LOST
Momentum –> Impulse
N2L:
F= ma —-> v/t = a
F=(delta m v)/t (force = rate of change of momenta)
(delta m v) = F (delta t)
Change in momentum = impulse
N1L:
momentum is constant if there is no external force (F=0 so F t =0)
change in momentum=0
[def] Principle of conservation of energy
“Energy cannot be created or destroyed, only transferred from one form to another”
Energy is a Scalar.
[def] Work, W
Work done by a force is the product of the magnitude of the force and the distance moved in the direction of the force.
W=F x cos(theta)
UNIT: J
[def] Potential Energy Ep: Definition and equation
Energy possessed by an object by virtue of its position
Ep = mgh
UNIT: J
[def] Kinetic energy, Ek: Definition and equation
Energy possessed by an object by virtue of its motion
Ek= ½m(v^2)
UNIT: J
[def] Elastic Potential Energy: Definition and equation
Energy possessed by an object when it has been deformed due to forces acting on it
Eelastic = ½Fx = ½ k(x^2)
k = spring constant, x = stretch or extension
UNIT: J
[def] Energy
The energy of a body or system is the amound of qork it can do
UNIT: J
[def] Power, P
Power is the work done per second, or energy transferred per second
or rate of work or rate of energy transfer
UNIT: W = J s-1
Work done equivalent to
Change in KE
Stability: more stable (x2)
Lower center of gravity
Wider base
Stability: equation
tan(theta) = w/h
Stability: when topple?
Object will topple when the center of gravity passes over the corner
Friction and drag re efficiency
Friction and drag –> energy transferred from system –> system’s efficiency decreases
