3.4.1.4 Projectile Motion

Question 1

What is friction?

Answer 1

Friction is a force that opposes motion.

Question 2

What are the two types of friction?

Answer 2

Dry friction

Fluid Friction.

Question 3

What is dry friction?

Answer 3

Friction between solid surfaces.

Question 4

What is fluid friction?

Answer 4

Known as drag, fluid resistance, or air resistance.

The friction of an object flowing through a fluid.

Question 5

What is a fluid?

Answer 5

A fluid is either a liquid or gas, something that can flow.

Question 6

What does the force though a fluid depend on?

Answer 6

The viscosity of thickness of the fluid.

Question 7

What happens to the friction as the speed increases?

Answer 7

As speed increases, the fluid friction increases.

Question 8

What is the relationship between fluid friction and surface area of the object

Answer 8

The larger the area pushing against the fluid, the greater the resistance force.

Question 9

What three things are key facts about frictional forces?

Answer 9

They always act in the opposite direction to the motion of the object.
They can never speed things up or start something moving.
They convert kinetic energy into heat and sound.

Question 10

What is lift?

Answer 10

Lift is an upwards force on an object moving through a fluid. It is perpendicular to fluid flow.

Question 11

When does lift happen?

Answer 11

It happens when the shape of an object causes the fluid flowing over it to changes direction.

Question 12

What is terminal speed?

Answer 12

Terminal speed is when the friction force equals the driving force.

Question 13

What are the conditions for an object to reach terminal (maximum speed)?

Answer 13

A driving force that stays the same all the time

A frictional force or drag force that increases with speed.

Question 14

What are the three main stages of reaching terminal speed for a car?

Answer 14

1) The car accelerates from rest using a constant driving force. The resultant force is in the greatest in the direction of motion.
2) As the speed increases, the frictional forces increases, This reduces the resultant force on the car and hence reduces its acceleration.
3) Eventually the car reaches a speed at which the frictional forces are equal to the driving force. There is now no resultant force and no acceleration, so the car carries on at a constant speed.

Question 15

What are the two ways of increasing a vehicles maximum speed?

Answer 15

Increasing the driving force, e.g. by increasing the engine size.

Reducing the frictional force, e.g. making the body more streamlined.

Question 16

What is the driving force for a parachutist?

Answer 16

The weight of the parachutist if the driving force.

Question 17

Explain the process of how a skydiver of parachutist can reach terminal speed.

Answer 17

1) A skydiver leaves a plane and will accelerate until the air resistance equals his weight.
2) He will then be travelling at a terminal speed.
3) However, the free fall speed is too high for them to safely land on the ground. He opens his parachute, which increases the air resistance massively, which slows him down to a lower terminal speed.
4) Before reaching the ground, he will open his parachute, which immediately increases the air resistance, so it is now nigger than his weight.
5) This slows him down until his speed has dropped enough for the air resistance to be equal to his weight again. This new terminal speed is small enough for him to land safely.