physical quantity
base quantities
derived quantity
a physical quantity that is not
dependent on other physical quantities
a physical quantity that is dependent
on other physical quantities
some base quantities
mass
amount of substance
length
time
temperature
electric current
light intensity
some derived quantities
displacement
area
volume
speed
velocity
work
energy
density
vector quantities
scalar quantities
a quantity that has both
magnitude and direction
a quantity that has only magnitude
some scalar quantities
distance
speed
mass
time
energy
volume
pressure
density
some vector quantities
displacement
velocity
acceleration
momentum
force
example:
5cm (distance)
example:
5cm to the right (displacement)
calculating vectors
by calculation
graphically
steps:
Choose a scale which fits the page For example, use 1 cm = 10 m or 1 cm = 1 N, so that the diagram is around 10cm
Draw the vectors at right angles to one another.
Complete the rectangle.
Draw the resultant vector diagonally from the origin.
Carefully measure the length of the resultant vector.
Use the scale factor to calculate the magnitude.
Use the protractor to measure the angle.
example:
PYTHAGORAS' THEOREM (hyp)² = (adj)² + (opp)²
steps:
- draw a vector diagram
- Calculate the magnitude of the resultant vector, using Pythagoras' Theorem.
- Calculate the direction of the resultant vector using trigonometry.
- State the final answer completes with direction.
Mass and weight
mass
weight
Mass is a measure of the quantity of matter in an object at rest relative to the observer.
mass is a scalar quantity
SI units: Kilogram (Kg)
for every Kg, there is 1000 grams
weight is a gravitational force on an object with mass
weight is a vector quantity
Si units: Newtons (N)
because of weight:
objects will always fall to the ground
objects stay firmly on the ground
satellites are kept in orbit
the weight of a body is equal
to the product of its mass (m) and the
acceleration of freefall (g)
we can find the mass of an object by using a scale
gravitational field strength
the force per unit mass acting on an objectin a gravitational field on earth
this is equal to 9.8N/Kg
density
mass per unit volume of a material
mass is found by using a scale
volume can be found by calculating with the appropriate equation if the shape is regular, or using a measuring cylinder ed with water for irregular objects
volume of a cube: L x W x H
volume of a cylinder: πr² x H
vomule of sphere: 4/3πr³