P5 Terminal Velocity (page 210)

Question 1

Why is it so hard that you can’t run into a hurricane whilst wearing a sandwich board?

Answer 1

It’s all to do with the air around you causing drag.

Question 2

If an object has no force propelling it along it will always slow down and stop, why?

Answer 2

because of fricion (unless you’re in space where there’s nothing to rub against).

Question 3

Friction always acts in the opposite direction to what?

Answer 3

movement.

Question 4

To travel at a steady speed, the driving force needs to balance what?

Answer 4

the frictional forces (see page 211).

Question 5

When do you get friction?

Answer 5

between two surfaces in contact, or when an object passes through fluid (drag).

Question 6

How can you reduce friction between surfaces?

Answer 6

by using a lubricant (see page 171).

Question 7

Friction speeds things up, or slows things down?

Answer 7

slows things down

Question 8

Do drag increase or decrease as speed increases?

Answer 8

increases as speed increases.

Question 9

What is ‘Drag’?

Answer 9

drag is the resistance you get in a fluid (a gas or a liquid). (air resistance is a type of drag).

Question 10

What is the most important factor by far in reducing drag?

Answer 10

the most important factor is keeping the shape of the object streamlined.

This is where the object is designed to allow fluid to flow easily across it, reducing drag, (parachutes work in the opposite way - they want as much drag as they can).

Question 11

Frictional forces from fluids always increase or decrease with speed?

Answer 11

they always increase with speed.

Question 12

A car has much more, or much less friction to work against when travelling at 70 mph compared to 30mph and why?

Answer 12

a car has much more friction to work against when travelling at 70 mph because at 70 mph the engine has to work much harder just to maintain a steady speed.

Question 13

When a falling object first sets off, is the force of gravity much more or much less than the frictional force slowing it down and why?

Answer 13

the force of gravity is much more than frictional force slowing it down, so it accelerates.

Question 14

What happens with friction when speed increases, and why?

Answer 14

the friction builds up., because theis gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force (so the resultant force is zero).

Question 15

Objects falling through fluids reach a terminal velocity.

When it has reached its maximum speed or terminal velocity what will the object do?

Answer 15

it will fall at a steady speed.

Question 16

What do terminal velocity depend on?

Answer 16

depends on shape and area.

Question 17

The less streamlined an object is the higher or lower its terminal velocity?

Answer 17

the lower its terminal velocity.

Question 18

Objects with large surface areas tend to have higher or lower terminal velocities?

Answer 18

Lower

Question 19

If you dropped a marble and a beach ball off a tall building, what objectterminal velocity would be higher? explain your answer

Answer 19

the marble’s terminal velocity would be higher than the terminal velocity of the beach ball.

This is because there is more air resistance acting on the beach ball, at any given speed.

So the beach ball spends less time accelerating (and so doesn’t speed up as much) before the air resistance is large enough to equal the accelerating force).

Question 20

Frictional forces are pretty much everywhere and they crop up again and again in physics, so makes sure you are comfortable talking about them. Then move onto explaining how drag affects an objects terminal velocity

Explain why a ball falling from the top of a tall building reaches terminal velocity (3 marks)

Answer 20

As the ball falls it accelerates towards earth due to the force of gravity (1 mark)

Air resistance means that eventually the resultant force on the ball is zero (1 mark)

The object cannot go any faster - this is its terminal velocity (1 mark).