forces in action

Question 1

what is the mass of an object

Answer 1

a physical property
the amount of matter it contains

Question 2

what is equilibrium

Answer 2

all the forces acting on an object in the same plane are balanced

Question 3

what is resultant force

Answer 3

a single force which has the same effect as the sum of all the forces acting on a body

Question 4

what is weight

Answer 4

the gravitiational force on a body measured in newtons

Question 5

what is newton

Answer 5

the force that causes a mass of one kg to hae an acceleration on one ms^-2

Question 6

what is inertia

Answer 6

the tendency of an object to continue in its sate of rest or in uniform motion unless acted upon by an external force

Question 7

what is the equation liking force mass and acceleration

Answer 7

F=ma
a force of one newton will give a 1kg mass an acceleration of 1ms^-2 in the direction of the force

Question 8

how do you work out the weight of an object

Answer 8

w=mg

Question 9

how can you determine the weight of an object

Answer 9

using a newtonmeter - shows the gravitational force acting on an object in newtons

Question 10

what is the centre of mass of an object

Answer 10

a point through which any externally applied force produces straight line motion but no rotation
the point at which the weight of the object may be considered to act

Question 11

what is the centre of gravity

Answer 11

an imaginary point at which the entire weight of an object appears to act

Question 12

how do you find the centre of gravity

Answer 12

a freely suspended object will come to rest with it centre of gravity vertically below the point of suspension
make small holes along the edges of the object
insert a pin through on the the holes and hold the pin firmly in a clamp
allow the object to swing freely and it will come to rest with its centre of gravity vertically below the pin
hang a plumb-line from the pin and draw a line along the vertical string of the plumb-line
repeat this process for other holes
the centre of gravity will be at the point of intersection of the lines
check the position of the centre of gravity by seeing if card will balance of a pin/finger

Question 13

what is the difference between the centre of mass and the centre of gravity on earth

Answer 13

nothing - they are the same point on earth

Question 14

what happens when an object topples over

Answer 14

the objects centre of gravity falls outside the base of the object
will topple as a moment (turning force) is introduced

Question 15

what is friction

Answer 15

the force that arises when two surfaces rub against eachother

Question 16

what is drag

Answer 16

the resistive force on an object travelling through a fluid

Question 17

what is tension

Answer 17

the force within a stretched cable or rope

Question 18

what is upthrust

Answer 18

an upward buoyancy force acting on an object when it is in a fluid

Question 19

what is normal contact force

Answer 19

a force arising when one object rests against another object

Question 20

what is a free body diagram

Answer 20

each force is represented by an arrow labelled with the force it represents
each arrow is drawn to the same scale - the longer the arrow the greater the force

Question 21

how do you work out the force parallel to the slope (Fx)

Answer 21

sin0 x W
sin 0 x mg

Question 22

how do you work out the force perpendicular to the slope (Fy)

Answer 22

cos0 x W
cos0 x mg`

Question 23

what is the component of the weight down the slope (Fx)

Answer 23

responsible for the acceleration of the object down the slope

Question 24

what is the component of weight perpendicular to the slope (Fy)

Answer 24

equal to the normal contact force

Question 25

what factors affect the drag experienced by an object

Answer 25

the speed of the object the cross sectional area of the object

Question 26

what is the relationship between dra and speed

Answer 26

drag force directly proportional to speed^2 when speed of object doubled the drag force increases by a factor of 4

Question 27

what is terminal velocity

Answer 27

the drag force on the object is equal and opposite to its weight object has zero acceleration and its speed is constant

Question 28

how does an object get to terminal velocity

Answer 28

instant the object starts to fall there is no drag force on the object, the total force is equal to the weight, the acceleration of the object is g - the acceleration of free fall as the object falls its speed increases and this in turn increases the magnitude of the opposing drag force, the resultant force on the object decreases and the instantaneous acceleration of the object becomes lass than g

Question 29

how do you find the net force of a falling object

Answer 29

mg-drag

Question 30

how do you find the acceleration of a falling object

Answer 30

a=(mg-d)/m

Question 31

what is the moment of a force

Answer 31

the turning effect of a force about some axis or point

Question 32

what is the equation for the moment of a force

Answer 32

moment=force x perp distance of the line of action of force from the axis or point of rotation moment = fx

Question 33

what s the SI unit for the moment of a force

Answer 33

Nm

Question 34

what happens when a body is in equilibrium

Answer 34

the net force acting on it is zero and its net moment is zero

Question 35

what is the principle of moments

Answer 35

for a body in equilibrium the sum of the anticlockwise moment about any point is equal to the sum of the clockwise moments about that same point

Question 36

what is a couple

Answer 36

a pair of equal and opposite forces acting on a body but not in the same straight line

Question 37

what is the torque of a couple

Answer 37

the turning moment of a couple torque = one of the forces x perp distance between them measure in Nm

Question 38

what is a triangle of forces

Answer 38

arrows are drawn to represent each of the three forces end-to-end the triangle is closed because the net force is zero and so the object is in equilibrium

Question 39

what is density of a substance

Answer 39

mass per unit volume

Question 40

what is the equation to calculate density

Answer 40

density=mass/volume p=m/v

Question 41

what is the si unit for density

Answer 41

kgm^-3

Question 42

how can you determine to density of a sbunstance

Answer 42

need to know mass and volume mass can be measured using a digital balance for liquids volume can be found using a measuring cylinder volume of regular shaped object can be calculated from measurements taken with a ruler, digital callipers or a micrometre volume of irregular solids can be determined by displacement of liquid - the volume is the difference between the liquid without and with the object in

Question 43

what is pressure

Answer 43

the normal force exerted per unit cross-sectional area

Question 44

what is the equation to calculate pressure

Answer 44

pressure=force/area p=F/A

Question 45

how do you calculate the pressure exerted by a vertical column of any liquid from its weight and the cross sectional area of the base

Answer 45

p=hroeg h is height of column roe is density g is acceleration of free fall

Question 46

how do you derive the equation p=hroeg

Answer 46

pressure at the base of the column equal to the weight W of the column divided by A W=mass of column x g the mass of the column is the density x volume W=(roeV) x g the volume of the column is Ah W=roe x Ah x g pressure is given by p=(roe x A x h x g)/A p=hroeg

Question 47

what does the equation of pressure in fluids show p=hroeg

Answer 47

pressure does not depend on the cross sectional area pressure proportional to height so water pressure increases with depth denser liquids will exert greater pressure

Question 48

why does an object float

Answer 48

upthrust is equal to the weight of the fluid displaced the weight if a floating object must be equal to the weight of the fluid it displaces

Question 49

what is archemides principle

Answer 49

the upthrust exerted on a body immersed in a fluid weather fully or partially submerged is equal to the weight of the fluid that the body displaces

Question 50

what happens when an object sinks

Answer 50

the upthrust is less than the weight of the object