Chapter 8- Modelling In mechanics

Question 1

Particle

Answer 1

Dimensions of the object are negligible

Question 2

Particle model assumptions

Answer 2

Mass of the object is concentrated at one point

Rotational forces and air resistance can be ignored

Question 3

Rod

Answer 3

All dimensions but one are negligible, like a pole or a beam

Question 4

Rod model assumptions

Answer 4

Mass is concentrated along a line
No thickness
Rigid (does not bend or buckle)

Question 5

Lamina

Answer 5

Object with area but negligible thickness, like a sheet of paper

Question 6

Lamina model assumptions

Answer 6

Mass is distributed across a flat surface

Question 7

Uniform body

Answer 7

Mass is distributed evenly

Question 8

Uniform body model assumptions

Answer 8

Mass of the object is concentrated at a single point at the geometrical centre of the body- the centre of mass

Question 9

Light object

Answer 9

Mass of the object is small compared to other masses, like a string or a pulley

Question 10

Light object model assumptions

Answer 10

Treat object as having zero mass

Tension is the same at both ends of a light string

Question 11

Inextensible string

Answer 11

A string that does not stretch under load

Question 12

Inextensible string model assumptions

Answer 12

Acceleration is the same in objects connected by a taut (tight) inextensible string

Question 13

Smooth surface model assumptions

Answer 13

Assume that there is no friction between the surface and any object on it

Question 14

Rough surface

Answer 14

When it is not smooth

Question 15

Rough surface model assumptions

Answer 15

Objects in contact with the surface experience a frictional force if they are moving or are acted by a force

Question 16

Wire

Answer 16

Rigid thin length of metal

Question 17

Wire

Answer 17

Treated as one-dimensional

Question 18

Smooth and light pulley

Answer 18

All pulleys you consider will be smooth and light

Question 19

Smooth and light pulley model assumptions

Answer 19

Pulley has no mass

Tension is the same on either side of the pulley

Question 20

Bead

Answer 20

Particle with a hole in it for threading on a wire or string.

Question 21

Bead model assumptions

Answer 21

Moves freely along a wire or string

Tension is the same on either side of the bead

Question 22

Peg

Answer 22

A support from which a body can be suspended or rested.

Question 23

Peg model assumptions

Answer 23

Dimensionless and fixed

Can be rough or smooth as specified in the question

Question 24

Air resistance

Answer 24

Resistance experienced as an object moves through the air.

Question 25

Air resistance model assumptions

Answer 25

Usually modelled as being negligible

Question 26

Gravity

Answer 26

Force of attraction between all objects. Acceleration due to gravity is denoted as g.

Question 27

Gravity model assumptions

Answer 27

All objects with mass are attracted towards Earth Earth's gravity is uniform and acts vertically downwards g is constant and is taken as 9.8m/s^2

Question 28

Normal reaction

Answer 28

This the force that acts perpendicular to a surface when an object is in contact with the surface.

Question 29

Friction

Answer 29

Force which opposes the motion between two rough surfaces

Question 30

Tension

Answer 30

The force acting on the object which is being pulled by a string is known as the tension (in the string).

Question 31

Thrust or compression

Answer 31

When an object is pushed by a light rod, the force acting on it is known as to the thrust r compression in the rod

Question 32

Buoyancy

Answer 32

Upward force on a body that allows it to float or rise when submerged in liquid

Question 33

Air resistance (force diagram)

Answer 33

Opposes motion.

Question 34

Displacement definition

Answer 34

Position relative to where you started from | Unit: metres

Question 35

Velocity definition

Answer 35

Rate of change of displacement | Unit: ms^-1

Question 36

Acceleration definition

Answer 36

Rate of change of velocity | Units: ms^-2

Question 37

Force/weight definition

Answer 37

Described by magnitude, direction and point of application | Units: Newton (N)

Question 38

Distance definition

Answer 38

Measure of length | Units: metres

Question 39

Speed definition

Answer 39

Measure of how quickly a body moves | Units: m/s

Question 40

Time definition

Answer 40

Measure of ongoing events taking place | Units: seconds

Question 41

Mass definition

Answer 41

Measure of the quantity of matter contained in an object | Unit: kg