Topic 1 – Physics and physical measurement

Scientific Notation We can express small and large numbers using scientific notation. This can be written as 6.02 x The number of atoms in 12 grams of carbon is approximately: 602,000,000,000,000,000,000,000

Order of magnitude We can say that the number 6 x is, to the nearest order of magnitude, Round to the nearest power of 10

Order of Magnitude Similarly, the length of a virus is 2.3 x meters. We can say to the nearest order of magnitude the length of a virus in meters is: is less than 5, so we round down to 10 -8

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 3 very small things.

Size Which is the biggest? What size is it, in meters (m), to the nearest order of magnitude?

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

Size On your paper write in order of increasing size the names of 3 very large things.

Size Which is the smallest? How small is it, in meters, to the nearest order of magnitude?

Size The largest object that you need to consider in physics is the Universe m The Universe has a size, to the nearest order of magnitude, of:

Ratio of biggest to smallest How much bigger is the universe than a proton? m m = times or 41 orders of magnitude bigger

Mass On your paper estimate the masses, in kilograms, of the 3 smallest objects you wrote down earlier.

Smallest mass The mass of the electron: kg! ( kg)

Biggest Mass We have already decided that the Universe is the largest object. What do you think its mass is? kg (100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 kg)

Ratio of most massive to least massive How much more massive is the universe than an electron? kg kg = times or 80 orders of magnitude bigger

Time Now think of 3 small time intervals (For example, the time it takes sound to travel 1 meter 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 meter is seconds to the nearest order of magnitude)

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

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

Time The age of the universe. Any ideas? seconds or 13.8 billion years

Ratio of longest to shortest How much longer has the universe existed than the time it takes light to cross a proton? s s = times or 41 orders of magnitude longer

Copy please! Size m to m (subatomic particles to the extent of the visible universe) Mass kg to kg (electron to the mass of the Universe) Time s to s (time for light to cross a nucleus to the age of the Universe)

One common ratio – Learn this! Hydrogen atom ≈ m Proton ≈ m Ratio of diameter of a hydrogen atom to its nucleus m m =10 5 times or 5 orders of magnitude bigger

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

Estimation/Guess What’s the difference?

Estimate the following: 1.The mass of an apple (to the nearest order of magnitude)

Estimate the following: 1.The mass of an apple 2.The time it takes your heart to beat 100 times. (to the nearest order of magnitude)

Estimate the following: 1.The mass of an apple 2. The time it takes your heart to beat 100 times. 3. The speed a cockroach can run. (to the nearest order of magnitude)

Estimate the following: 1. The mass of an apple 2. The time it takes your heart to beat 100 times. 3. The speed a cockroach can run. 4. The number of times the earth will fit into the sun (R s = 6.96 x 10 8 m, R e = 6.35 x 10 6 m) (to the nearest order of magnitude) kg 10 2 s 10 0 m/s (6.96 x 10 8 m) 3 (6.35 x 10 6 m) 3 =10 6

Let’s do some more estimating!