Measurements Physics

Does Physics make you feel like this?

Do you think? Physics is difficult You need to be a genius with Maths There are loads of formulae you have to learn.

Well, YOU ARE WRONG!!! If you try to learn Physics like a parrot, blindly learning facts without thinking what they mean, Physics is hard.  If, however, you think about what it means, you will soon see that Physics is a logical subject that describes how things are related.  You will find that a lot of things do relate, which you might not have expected.  Physics fits together like a jigsaw puzzle.

But why all those numbers and formulas then? Physics is a quantitative science.  That means that it works with numbers.  Many relationships in Physics are numerical. Formulae are simply the rules of Physics written in shorthand.  Each quantity in Physics is given a symbol 

Do you know what units are used to measure them? Quantities in physics Before a mesurement can be made a standard or unit must be chosen You can then find the quantity of what you are trying to measure The three main quantities in physics are Length Mass Time Do you know what units are used to measure them?

Units of length? Mile, furlong, fathom, yard, feet, inches, Angstroms, nautical miles, cubits

SI Units The SI system is now used in many countries It is a decimal system in which units are divided or multiplied by 10 to give smaller or larger units Group Activity: How many SI units do you already know of as a group?

The SI system of units There are seven fundamental base units which are clearly defined and on which all other derived units are based: You don’t need to know how these are defined

Units of length?

The metre This is the unit of distance. It is the distance traveled by light in a vacuum in a time of 1/299792458 seconds.

The second This is the unit of time. A second is the duration of 9192631770 full oscillations of the electromagnetic radiation emitted in a transition between two hyperfine energy levels in the ground state of a caesium-133 atom.

The ampere This is the unit of electrical current. It is defined as that current which, when flowing in two parallel conductors 1 m apart, produces a force of 2 x 10-7 N on a length of 1 m of the conductors.

The kelvin This is the unit of temperature. It is 1/273.16 of the thermodynamic temperature of the triple point of water.

The mole One mole of a substance contains as many molecules as there are atoms in 12 g of carbon-12. This special number of molecules is called Avogadro’s number and equals 6.02 x 1023.

The candela (not used in AS) This is the unit of luminous intensity. It is the intensity of a source of frequency 5.40 x 1014 Hz emitting 1/683 W per steradian.

The kilogram This is the unit of mass. It is the mass of a certain quantity of a platinum-iridium alloy kept at the Bureau International des Poids et Mesures in France. THE kilogram!

You will need to know these? SI Base Units You will need to know these? Quantity Unit distance metre time second current ampere temperature kelvin quantity of substance mole luminous intensity candela mass kilogram Note: No Newton or Coulomb

Length metre (m) The unit of length is _________________ 10 mm = __________ cm 100 cm = __________ m 1000 m = ___________ km 1 micrometer = __________ m 1 nanometer =_________m 1 1 1 0.000001 0.000,000,001

Ranges of sizes, masses and times

These numbers are CRAZY!! In Physics you deal with very small and very large quantities Therefore we use Standard Notation as a quick way of writing numbers with lots of zeros Try the Standard Notation exercises in your booklet and see how you get on!

Order of magnitude We can express small and large numbers using exponential notation The number of atoms in 12g of carbon is approximately 600000000000000000000000 This can be written as 6 x 1023

Order of magnitude We can say to the nearest order of magnitude that the number of atoms in 12g of carbon is 1024 (6 x 1023 is 1 x 1024 to one significant figure)

Small numbers Similarly the length of a virus is 2.3 x 10-8 m. We can say to the nearest order of magnitude the length of a virus is 10-8 m.

Ranges of sizes, masses and times You need to have an idea of the ranges of sizes, masses and times that occur in the universe.

Size On your paper can you write in order of decreasing size the names of 5 very small things.

Size Which is the smallest? What size is it to the nearest order of magnitude?

Size The smallest objects that you need to consider AS IB physics are subatomic particles (protons and neutrons). These have a size (to the nearest order of magnitude) of 10-15 m.

Size On your paper can you write in order of increasing size the names of 5 very large things.

Size Which is the largest? How large is it to the nearest order of magnitude?

Size The largest object that you need to consider in AS physics is the Universe. The Universe has a size (to the nearest order of magnitude) of 1025 m.

Mass On your paper can you estimate the masses of the 5 smallest objects you wrote down earlier.

10-30 kg! Mass What do you think the mass of the electron is?

Mass We have already decided that the Universe is the largest object. What do you think its mass is? 1050 kg (100000000000000000000000000000000000000000000000000 kg)

Time Now think of 5 small time intervals (For example, the time it takes sound to travel 1 metre is a small time interval. Can you think of smaller?)

Time Can you add order of magnitude estimates for your time intervals? (For example, the time it takes sound to travel 1 metre is 10-3 seconds to the nearest order of magnitude)

Time The smallest time interval you need to know is the time it takes light to travel across a nucleus. Can you estimate it? 10-23 seconds

Time What’s the longest time interval you can think of?

Time The age of the universe. Any ideas?

Time The age of the universe. 1018 seconds

Ranges Size 10-15 m to 1025 m (subatomic particles to the extent of the visible universe) Mass 10-30 kg to 1050 kg (electron to the mass of the Universe) Time 10-23 s to 1018 s (time for light to cross a nucleus to the age of the Universe)

A common ratio Hydrogen atom ≈ 10-10 m Proton ≈ 10-15 m Ratio of diameter of a hydrogen atom to its nucleus = 10-10/10-15 = 105

Estimation You have to be able to make order of magnitude estimates.

Estimation/Guess What’s the difference?

Estimate the following: (to the nearest order of magnitude) The mass of an apple

Estimate the following: (to the nearest order of magnitude) The mass of an apple The number of times a human heart beats in a lifetime.

Estimate the following: (to the nearest order of magnitude) The mass of an apple The number of times a human heart beats in a lifetime. The speed a cockroach can run.

Estimate the following: (to the nearest order of magnitude) The mass of an apple The number of times a human heart beats in a lifetime. The speed a cockroach can run. The number of times the earth will fit into the sun (Rs = 6.96 x 108, Re = 6.35 x 106)

Estimate the following: (to the nearest order of magnitude) The mass of an apple The number of times a human heart beats in a lifetime. The speed a cockroach can run. The number of times the earth will fit into the sun (Rs = 6.96 x 108, Re = 6.35 x 106)

Estimate the following: (to the nearest order of magnitude) The mass of an apple 10-1 kg The number of times a human heart beats in a lifetime. The speed a cockroach can run. The number of times the earth will fit into the sun (Rs = 6.96 x 108, Re = 6.35 x 106)

Estimate the following: (to the nearest order of magnitude) The mass of an apple 10-1 kg The number of times a human heart beats in a lifetime. 70x60x24x365x70=109 The speed a cockroach can run. The number of times the earth will fit into the sun (Rs = 6.96 x 108, Re = 6.35 x 106)

Estimate the following: (to the nearest order of magnitude) The mass of an apple 10-1 kg The number of times a human heart beats in a lifetime. 70x60x24x365x70=109 The speed a cockroach can run. 100 m/s The number of times the earth will fit into the sun (Rs = 6.96 x 108, Re = 6.35 x 106)

Estimate the following: (to the nearest order of magnitude) The mass of an apple 10-1 kg The number of times a human heart beats in a lifetime. 70x60x24x365x70=109 The speed a cockroach can run. 100 m/s The number of times the earth will fit into the sun (6.96 x 108)3/(6.35 x 106)3 = 106

Estimate the following: (to the nearest order of magnitude) The mass of an apple 10-1 kg The number of times a human heart beats in a lifetime. 70x60x24x365x70=109 The speed a cockroach can run. 100 m/s The number of times the earth will fit into the sun (6.96 x 108)3/(6.35 x 106)3 = 106

Let’s do some more estimating!

Mass Mass:- It is the measure of amount of matter in a given object The Unit of mass in SI unit is Kilogram 1000 mg = 1 g 1000 g = 1 Kg The terms weight and mass are not same

Time Time is a duration The unit of time is second(s) The time measuring devices rely on some kind of constantly repeating oscillations. In digital clocks and watches the oscillations are produced by a tiny quartz crystal.

Measurements in Physics Watch this short video clip and be ready to share your thoughts afterwards

Most commonly used prefixes in Physics Factor Symbol Mega- ( mostly used for radio station frequencies) x 106 M Kilo- ( used for just about anything, Europe uses the Kilometer instead of the mile on its roads) x 103 K Centi- ( Used significantly to express small distances in optics. This is the unit MOST people in AP forget to convert) x 10-2 c Milli- ( Used sometimes to express small distances) x 10-3 m Micro- ( Used mostly in electronics to express the value of a charge or capacitor) x 10-6 Nano ( Used to express the distance between wave crests when dealing with light and the electromagnetic spectrum) x 10-9 n