1.1 - Basic physics Flashcards
What is the unit for:
mass
length
time
electrical current
temp
amount of a substance
luminous intensity
m
l
t
I
T
n (mol)
L
Derive unit of area of a rectangle
= length x breadth
=Unit of breadth x Unit of length
=m x m = m2
Derive unit of change of speed (velocity)
=final speed - initial speed
= 33ms-1 - 15ms-1
= 18ms-1 (remember 33a - 15a = 18a)
so unit of change of speed = unit of speed
Derive the unit of acceleration
= change in velocity/ time
ms-1 / s = ms-2
Express ____ in SI units
Force = mass x accel
Work= force x distance
Power = work / time
N = kg ms-2
J= kg m2 s-2
W = kg m2 s-3
The drag force FD, on sphere moving through a fluid is given by FD=6(pi)nav, where a is the radius of the sphere, v the velocity and n is the coefficient of the viscosity of the fluid. Find the unit of n in terms of the base SI units
Rearrange, n = FD/6(pi)av
6 and (pi) have no units, so,
n = FD/ av
FD= kg ms-2
a = m
v = m s-1
n = kg m s-2/ m2 s-1
n = kg m-1 s-1
Remember ( a5 / a3 = a2)
Consider the equation v2 = u2 + 2ax and test if it is homogenous
u2 term = (m s-1)2 = m2 s-2
2ax term = (m s-2 x m) = m2 s-2
u2 term and 2ax term have same units, means they can be added together, unit of right side of equation = m2 s-2
v2 term = (m s-1)2 = m2 s-2
left side same unit as right side. things can only be equal if they have the same units
What does homogenous mean?
only terms with the same units are added or subtracted and the units of the 2 sides are the same
What is a scalar quantity?
is a quantity with magnitude only
What is a vector quantity?
is a quantity that has magnitude and direction
What is a resultant force?
The combined effect of two or more forces
What is the cosine and sine rule?
a2 = b2 + c2 -2bcCOS(A)
SIN(A) / a = SIN(B) / b
Give some examples of scalar quantities
mass, volume, area, distance, length, speed, work, time
Give some examples of vector quantities
displacement, velocity, acceleration, force, momentum
What is displacement?
change in position of an object
