Is it easier to ski on grass or snow ?, Why ?
To ski on snow , as the snow is smooth ,The friction force depends on the type of the material directly in contact with the base of the snow scooter.
It is a type of friction force that happens when a body moves through air.
Air resistance
The force between two surfaces in contact that acts in a direction opposite to the direction of motion and causes the object to slow down and stop.
Friction force.
The fish has streamline shape.
To decrease the surface area, so the water resistance decreases.
It is a type of friction force that happens when a body moves through water.
Water resistance.
Air crafts are desighned in streamline shape.
To decrease the surface area , so the air resistance decrease, and the speed increase.
Parachutist opens the parachute on landing.
to increase surface area that increase air resistance , and slow down his motion to land safely.