The most common hydrogen isotope, protium, has no neutrons in the nucleus.
Isotopes of
The state of matter that has particles that slide by one another is liquid because liquid is very slippery.
Yes it is valid all the times under the consideration of acceleration due to gravity .it is not valid on space where there is no influence of gravity
Free fall means your falling because of gravity and weight and will eventually hit the ground without any protection. weightlessness means a place or time where there is no gravity and you're floating and not falling.
When speed is combined with strength it is power