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