Forces In Action Flashcards Preview

AS Physics > Forces In Action > Flashcards

Flashcards in Forces In Action Deck (37):
1

Equation for weight

W=mg

2

Tension

A force experienced by a string or wire that is being pulled

3

Normal contact force

A force that acts perpendicular to the point of contact between two surfaces

4

Upthrust

The upward force that a liquid or gas exerts on a body due to the liquid or gas being displaced

5

Friction

A force that occurs between two surfaces that opposes motion. It is a result of intermolecular forces.

6

What you show on a free body diagram (3)

- The bodies
- The directions of each force
- The value of each force

7

Fluid

A liquid or a gas

8

Drag

The frictional force experienced by an object travelling through a fluid

9

Does friction depend on velocity

no

10

Does drag depend on velocity

yes

11

Factors affecting drag (4)

- Density of fluid
- Coefficient of drag
- Cross sectional area of object
- Velocity

12

The motion of an object falling in the presence of drag

- Initially accelerates because force of gravity acts downwards and there is minimal drag
- As speed increases the upwards force of drag increases
- Eventually the force of weight is equal to the force of drag and the object no longer accelerates and is moving at its terminal velocity

13

What happens when a parachute is opened while falling at terminal velocity

The drag force increases due to the increased cross sectional area. This results in a net upwards force and therefore an upwards acceleration, which causes the skydiver to slow down. As they slow down the drag force decreases until a new terminal velocity is reached

14

Terminal velocity

The speed of an object at which the weight is equal to the drag

15

Experiment to determine terminal velocity of a body in a fluid

Set up a cylinder filled with fluid and wrap elastic bands around it at regular intervals. Drop a ball of known mass into the tube and time how long it takes to reach each elastic band. Towards the bottom the times should remain constant and this value is used to calculate terminal velocity

16

Equilibrium

The resultant force acting on an object is zero

17

How to find the resultant of two forces

Add

18

Moment

The turning effect of a force

19

Equation for a moment

moment = force * perpendicular distance

20

Principle of moments

For a body to be in equilibrium, the sum of the clockwise components must equal the sum of the anticlockwise components

21

Principle of moments

For a body to be in equilibrium, the sum of the clockwise components must equal the sum of the anticlockwise components

22

Couple

Pair of forces of equal size that act in parallel but opposite directions, resulting in a turning force (torque)

23

Equation for torque of a couple

T = (magnitude of one force) * (perpendicular distance between the forces)

24

Weight

Force experienced by a mass due to a gravitational field

25

Centre of mass

A single point that you can consider the entire mass to exist at, regardless of orientation

26

Centre of gravity

A single point through which the entire weight of an object can be thought to act

27

When are the centre of mass and the centre of gravity the same

For a small body in a uniform gravitational field

28

Experiment to find centre of gravity

Hang the object freely from a point and draw a vertical line down it. Repeat from another point. Where these two lines cross will be the centre of gravity

29

Three forces act on an object in equilibrium. What must these forces be?

coplanar

30

Density

Mass per unit volume

31

Pressure

Force per unit area

32

Unit of pressure

Pascal (Newtons per metre squared)

33

Pressure in a fluid

p=hρg
p - pressure
h - depth
ρ - density
g - acceleration due to gravity

34

Upthrust

An upward force exerted by a fluid on an object that is fully or partially submerged

35

Archimedes principle

The upthrust is equal to the weight of fluid displaced

36

Equation for upthrust

F = (h2 - h1)ρgA
or
F = sρgA where s is the height of the object

37

Remember

Pressure increases as you go deeper into a fluid but upthrust is the same wherever you are (as long as you are fully submerged)