2 - Foundations of Physics Flashcards
What is a quantity?
A property of an object or phenomenon that can be measured.
What are the 6 (total 7) SI base quantities/units that you need to know?
length, mass, time, electric current, temperature, amount of a substance, (light intensity)
What is the unit and symbol for distance?
metre, m
What is the unit and symbol for mass?
kilogram, kg
What is the unit and symbol for time?
second, s
What is the unit and symbol for electric current?
ampere, A
What is the unit and symbol for temperature?
kelvin, K
What is the unit and symbol for amount of a substance?
mole, mol
Why is a unit symbol sometimes written in upper case?
Because it was named after a person (but the unit name is always lower case)
What do we use to measure quantities other than the 7 base quantities?
Derived units
How do we work out derived units?
From the base units and the equations which relate the derived quantities to the base quantities.
What is a scalar quantity?
A quantity with magnitude but no direction.
What is a vector quantity?
A quantity with magnitude and direction.
What does it mean if an equation is homogeneous?
Both sides of the equation have the same SI units.
What is an uncertainty?
How sure we can be about a measurement.
What do you do when you take multiple measurements?
Find the average to find the actual value.
What is the absolute uncertainty?
Half of the range.
How do you work out an uncertainty?
Find the average. Then find half of the range.
AVG+-HALF RANGE
How do you work out a percentage uncertainty?
Find the average. Find out half of the range as a percentage of the average.
AVG+- (HALF RANGE / AVG x 100)
What is a true value?
A value that would be obtained in an ideal measurement. The values that you expect to get in an experiment.
What is a random error and what causes them?
A measurement error which varies unpredictibly. They can occur due to factors that are not controlled in the experiment / difficulty in reading the measurement device.
What is a systematic error and what causes them?
A measurement error in which the measurement differs from the true value by the same amount each time. They can occur due to the way measurements are taken / faulty measuring devices.
Give a difference between a random error and a systematic error.
Systematic errors can be corrected.
What do you do to the uncertainty when you add or subtract two quantities?
Add the absolute uncertainties.
What do you do to the uncertainty when you multiply or divide two quantities?
Add the percentage uncertainties.
What do you do to the uncertainty when you raise a quantity to a power (n)?
Multiply the uncertainty by (n).
How do you calculate vectors in a straight line?
Add or subtract (depending on direction)
How do you calculate perpendicular vectors?
Use Pythagoras theorem.
What steps do you follow to solve vector problems?
- Break down into horizontal and vertical components
- Add/subtract all parallel vectors
- Use Pythagoras to work out the resultant force.
