P3.2 Using physics to make things work Flashcards Preview

Physics - P3 > P3.2 Using physics to make things work > Flashcards

Flashcards in P3.2 Using physics to make things work Deck (47):
1

If an object is freely suspended, an object will come to rest with its....

centre of mass directly below the point of suspension

2

Where the the centre of mass in a symmetrical object?

along the axis of symmetry

3

In the equation

T = 1 (divided by) f

what does each letter stand for and what are the units?

T - periodic time - time period (s)

f - frequency (Hz)

4

Describe a simple pendulum

suspending a weight from a piece of string.

when you let it go, it will swing back and forth

5

What is the time period of a pendulum?

The time taken for the pendulum to swing from one side to the other and back again

6

What does the time period of a pendulum depend on?

the length of the pendulum

the longer the length of the pendulum, the greater the time period

the shorter the length of the pendulum, the shorter the time period

7

What are some applications of a pendulum?

old-style clocks

playground swings

fairground rides

8

What is the turning effect of a force called?

the moment

9

In the equation

M = F X d

what does each letter stand for and what are the units?

M- moment of the force (Nm)

F- force (N)

d- perpendicular distance from the line of action of the force to the pivot (m)

10

Describe the moments if an object is not turning

the total clockwise moment must be exactly balanced by the total anticlockwise moment about any pivot

11

If the anticlockwise moments are equal to the clockwise moments.....

the object wont turn

12

How do levers make it easier to do work?

they move the distance the force is applied further from the pivot

13

Give some example of simple levers as force multipliers

long sticks or bars

wheelbarrows

scissors

14

How are force multipliers helpful?

they increase the distance from the pivot at which force is applied

this means less force is needed to get the same moment

levers reduces the amount of force that's needed to get the same moment by increasing the distance

15

When will an object topple over?

if the line of action of the weight of an object lies outside the base of the object (if centre of mass moves beyond edge of base) there will be a resultant moment causing the object to topple

this is because the total anticlockwise moments do not equal the total clockwise moments, causing a resultant moment

16

The most stable objects have a .....

wide base and low centre of mass

17

Why does a bunsen burner have a wide heavy base?

to give it a low centre of mass - heavier to knock over

18

Liquids are virtually ....

incompressible

19

What does it mean that liquids are virtually incompressible?

you can't squash them, their volume and density stay the same

20

What will happen when you apply a force to one point in a liquid, why?

the pressure in the liquid is transmitted equally in all directions

(the force exerted at one point on a liquid will be transmitted to other points in the liquid)

This is because liquids are virtually incompressible and can flow

21

In the equation

P = F (divided by) A

what does each letter stand for and what are the units?

P- pressure in pascals (Pa)

F- force (N)

A- cross sectional area (m2)

22

What are hydraulic systems used as?

force multipliers - they use a small force to produce a bigger force

23

Describe a simple hydraulic system

2 pistons, one with a smaller cross sectional area than the other

Pressure is transmitted equally through a liquid so the pressure at both pistons is the same

At the first piston, a pressure is exerted on the liquid using a small force over a small area

This pressure is transmitted to the second piston

The second piston has a larger surface area and so (as force = pressure x area) there will be a larger force

24

Where are hydraulic systems used?

car braking systems

25

What happens when an object moves in a circle?

it continually accelerates towards the centre of the circle

This acceleration changes the direction of motion of the body, not its speed

26

What is the force called that keeps something moving in a circle?

a centripetal force

27

What direction is the centripetal force on an object which is moving in a circle?

the centripetal force is always towards the centre of the circle

28

What force provides the centripetal force when a car goes around a bend?

friction

29

What force provides the centripetal force when a bucket is whirled around a rope?

Tension in the rope

30

What force provides the centripetal force in a spinning fairground ride?

tension

31

The centripetal force needed to make an object perform circular motion increases as:

the mass of an object increases

the speed of an object increases

the radius of the circle decreases

32

What kind of objects may be unstable?

those with a narrow base and a high centre of mass

33

A centripetal force......................... but is always provided by something else such as gravitational force, friction or tension

does not exist in its own right

34

What is the centre of mass of an object?

The point at which the mass of the object may be thought to be concentrated

35

The ....... an object is moving, the bigger the centripetal force needed to keep it moving in a circle

faster

36

The .... the mass of an object, the bigger the centripetal force needed to keep it moving in a circle

Larger

37

The ...... the radius of a circle an objects moving in, the bigger the centripetal force needed to keep it moving in a circle

smaller

38

Describe how to find the centre of mass for an object that is not a regular shape

- suspend it from a point around its edge

- mark a vertical line directly under the point of suspension

- repeat 2 more times

- the centre of mass is where these points cross

39

Explain why double decker buses are less stable than single deck buses

the centre of mass is higher above the ground for a double decker bus.

It is more likely to lie outside the base of the bus

40

The time period of a pendulum does not depend on ....

the mass of the object or the amplitude of the swing

41

What are moments measured in?

Nm (Newton meters)

42

What is pressure measured in?

Pa (pascals)

43

What provides the centripetal force that keeps planets and satellites in orbit?

gravity

44

Describe the movement of a simple pendulum

swings back and forth

at the highest point of its swing, the pendulum briefly stops and stores energy as gravitational potential energy

at the lowest point of the swing, this energy is transferred to kinetic energy as the pendulum travels fastest

45

Explain how the centripetal force changes when a car slows down as it drives around a bend

the force decreases because centripetal forces are less when the speed is lower

46

Explain how the centripetal force changes when a bucket of water is swung around in circles when it is full of water and when it is empty

the force is greater when the moving mass is larger

47

Explain how the cylinder is rotating at a constant speed but at the same time the riders inside the cylinder are accelerating

The direction of the riders is constantly changing

therefore the velocity of the riders is changing

and because acceleration is the rate of change of velocity, the acceleration is changing