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Chapter 3 -- Part 2
Let's assume that a jumper jumps from a full speed of 10 m/s.
The estimate is in line with the current world record of about 9 m for men and 7.5 m for women.
We have neglected the effect of air resistance on the motion of objects, but we know from experience that this is not a negligible effect.
The air has to be pushed out of the way when an object moves.
The force of the reaction pushes back on the body and causes it to slow down.
We can see some of the properties of air by sticking our hand outside a car.
The larger the air force, the greater it is.
The force is greater when the palms face the direction of motion.
The force increases with the direction of motion.
As the body gains speed, the air resistance grows and the net force on the body decreases.
The force due to air resistance is equal to the weight if the body falls from a great height.
The solution of 3.22 is not constant and can't be obtained with simple techniques.
The terminal velocity can be obtained without difficulty.
The downward force of gravity is canceled by the upward force of air resistance at the terminal velocity.
The square root of the linear size of the objects determines the terminal velocity of different-sized objects that have a similar density and shape.
The following argument shows this.
Implications on the ability of animals to survive a fall have arisen from this result.
This is the speed at which any animal can hit the ground without injury.
The force of air resistance on an animal the size of a man is insignificant compared to the weight.
A small animal is slowed down by air.
It is possible for a small creature to drop from a height.
Rats are rarely encountered in deep coal mines.
A calculation shows that a mouse can fall down a mine shaft.
A fall will kill a rat.
There is an effect on the speed of falling precipitation.
A 1- cm diameter hailstone falling from a height of 1000 m would hit the Earth at a speed of 140 m/s.
The hailstone would hurt anyone that it fell on.
Muscular movement is what animals do.
The chemical energy in the food eaten by the animal allows the work to be performed.
Only a small portion of the energy consumed by the muscles is converted to work.
The efficiency of the muscles is 20% in bicycling at a rate of one leg extension per second.
One fifth of the chemical energy consumed by the muscle is converted to work.
As heat, the rest is dissipated.
The metabolism is the amount of energy consumed per unit time.
The type of work and the muscles involved affect muscle efficiency.
In most cases, the efficiency of the muscles is less than 20%.
We will assume a 20% muscular efficiency in our calculations.
We will calculate the amount of energy consumed by a person jumping up 60 cm for 10 minutes at a rate of one jump per second.
The doughnuts have energy content in them.
The metabolic rate is calculated by A. H. Cromer while running.
This is in agreement with the measurement.
The difference between work and muscular effort should be noted in connection with the energy consumption during physical activity.
Work is defined as the product of force and the distance over which the force acts.
The wall does not move when a person pushes against it.
The act of pushing uses a lot of energy.
All the energy is spent in the body to keep the muscles balanced.
A 70 kilogram man can only jump to a height of 10 cm because of the heavy equipment he has.
The conditions of the jump are described in the text.
Consider a person on the moon who does a broad jump.
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