Chapter 4 - Forces in action

Question 1

Define the newton

Answer 1

The force that will give a mass of 1kg an acceleration of 1m/s

Question 2

Definition of weight

Answer 2

Gravitational force acting on an object, through it’s centre of mass

Question 3

Definition of friction

Answer 3

the force that arises when two surfaces rub together

Question 4

Define drag

Answer 4

the resistive force on an object travelling through a fluid

Question 5

Define tension

Answer 5

the force within a stretched cable or rope

Question 6

define up-thrust

Answer 6

the upward buoyancy force acting upon an object when it is fully or partly submerged in a fluid.

Question 7

define normal (reaction) contact force

Answer 7

the force arising when an object rests against another object acting perpendicular to the plane of contact

Question 8

How should you resolve forces of sloped free body diagrams

Answer 8

parallel and perpendicular to the slope

Question 9

Factors effecting drag

Answer 9

• speed of the object
• shape and texture
• cross sectional surface area
• density of the fluid

Question 10

Define and outline terminal velocity

Answer 10

• As the velocity of an object increases during free fall, so does the magnitude of the drag force
• As the weight of the object remains constant, the net force will be reduced until 0.
• The acceleration is proportional to the net force acting on it
• So as the net force reduces, so does the acceleration
• At the point where the drag force = the weight, the net force is zero so the acceleration = 0.
• This is terminal velocity.

Question 11

Define moment of a force with SI units

Answer 11

• the magnitude of the force x the perpendicular distance from the pivot, moment = Fx,
• it is the turning affect of the force about an axis or pivot
• Nm
  SI = kgm^2s^-2

Question 12

When will a force not produce a moment?

Answer 12

Force is acting on the pivot, so x = 0 or when the force is acting parallel to the pivot

Question 13

what is a couple and define it

Answer 13

A pair of forces that have equal magnitude but act in opposite direction. The product of one of the forces and the perpendicular distance between the forces.

Question 14

Principle of moments

Answer 14

for a body in equilibrium, the sum of the clockwise moments equals the sum of the anticlockwise moments about the same point.

Question 15

Define centre of mass

Answer 15

the point at which the weight acts

Question 16

define density

Answer 16

mass per unit volume

Question 17

how to find the volume of an irregular solid

Answer 17

• submerge in water in measuring cylinder

- change in volume equals the volume of the solid

Question 18

define pressure

Answer 18

normal force exerted on a service area per unit cross sectional area (Pa)

Question 19

equation for pressure at bottom of a cylinder

Answer 19

p = height * density of fluid * gravity

Question 20

explain and define Archimedes principle and the situation of a floating object.

Answer 20

When an object is submerged in a fluid, it experiences an upwards force, called upthrust, because the pressure at the bottom surface of the object is greater than at the top surface. Therefore the upthrust exerted on a body immersed in a fluid, whether partially or fully submerged, is equal to the weight of the fluid that the body displaces. For a floating object, the weight = upthrust, so weight = the weight of the fluid displaced.