# Evan's Space

## Wonders of Physics ## Physical Quantities Videos

The smallest to the biggest thing in the universe.
This video shows the various prefixes used to denote very small or big numbers.

Is Usain Bolt faster than a typical car on the road with a constant speed of 60 km/h?
Calculate the average speed of Usain Bolt for the 100 m world record of 9.58 s in m/s. Then convert it to km/h to do a comparison.

Wanna watch his 200 m race?

How to use a vernier caliper?
The precision of vernier caliper is 0.01 cm (0.001 m).

How to use a micrometer screw gauge?
The precision of the micrometer is 0.01 mm

Factors that affect the period of the pendulum bob
Only length and gravitational field strength (g) affect the period.
– Length of pendulum increases, period (T) is longer
– Gravitational field strength (g) decreases, period (T) is longer (i.e. on the moon)

Mass of pendulum bob and angle of release (5 to 10 degree) will not affect the period (T).

## Density (Units Conversion) and Floatation

Density is the mass per unit volume.

Common units for density are g/cm3 or kg/m3. SI unit is kg/m3.

Density of a pure substance is fixed, regardless of it’s size! Floating and Sinking

A denser (heavier) substance will sink in liquid which is less denser (lighter).
A less dense substance will float in a liquid which is denser.
If substance has the same density as the liquid, it will be suspended in the liquid.

## Conversion of m/s to km/h and vice versa – Usain Bolt’s world record for 100m

Usain Bolt smashed the 100m and 200m World record with a time of 9.58 s and 19.19s respectively in Berlin 2009! Can’t embed the 100m clip here. So just how fast is he? Is he much faster than your dad’s car on the expressway 90 km/h???

100m in 9.58s means approx. 10.44 m/s = 37.58 km/h. So well, 2 legs are slower than 4 wheels =) How do you convert?

View the step by step conversion from m/s to km/h. (in short, multiply by 3.6)

Below is another record set by him. 200m in 19.19s. You can try to do the conversion!