Flashcards in Chapter 4, Forces Deck (24):

1

## Defining equation for force?

### F=ma (force=mass*acceleration).

2

## Unit for force?

### Newtons.

3

## Difference between mass and weight?

### Mass (measured in kg) is how much stuff there is, weight (measured in N) is the product of mass and g and gives the force applied to an object towards the centre of mass of the object it is in the gravitational field of.

4

## What is the centre of mass?

### The point in an object through which weight acts, also if a force is applied through the centre of mass there is no net moment.

5

## How do you find the centre of mass of an object?

### if you hang an object from a point you know the line through the point which is perpendicular to the earth goes through the centre of mass. You can use a plumb-line to help measure this position.

6

## What is weight?

### The gravitational force acting through the centre of mass of an object.

7

## What is friction?

### The resistive force from two rough objects rubbing against each other.

8

## What is drag?

### The resistive force acting on an object travelling through a fluid.

9

## What is tension?

### The force within a stretched object (usually string/rope)

10

## What is upthrust?

### An upwards force acting on an object inside a fluid caused by the displacement of this fluid.

11

## What is the normal contact force?

### The force acting 90 degrees to the surface an object is resting on stopping it falling through the object.

12

## On a smooth slope with an object resting on it what is the value of the normal contact force and the component of the weight down the slope?

### Normal contact = component of weight perpendicular to slope = mg*cos(theta), component of weight down slope = mg*sin(theta).

13

## What are the main factors that is drag proportional to?

### Speed of the object and cross sectional area, also shape of object, roughness/texture of object and the density and viscosity of the fluid.

14

## What is terminal velocity?

### The point of equilibrium between weight and the drag force such that the net force is 0.

15

## What is the equation for the moment of a force?

### moment = force * perpendicular distance.

16

## Unit for moments?

### Newton meters.

17

## What is the principle of moments?

### For a body in rotational equilibrium the sum of the anticlockwise moments about a point is equal to the sum of the clockwise moments about that same point.

18

## What is a couple?

### Two equal forces acting in opposite directions about a point such that it rotates without having any displacement.

19

## What is the defining equation for density?

### ρ = m/V (density = mass/volume).

20

## What is the defining equation for pressure?

### p = F/A (pressure = force/area).

21

## What is the unit for pressure?

### The Pascal (Pa).

22

## What does the equation p=hρg show?

### pressure = height fluid column * density of liquid * acceleration due to gravity.

23

## What is the equation for upthrust?

### upthrust = Axρg where A is the area on top, x is the height of the submerged object, ρ is pressure and g is acceleration due to gravity.

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