Module 3.2 Flashcards
Archimede’s priciple
The upwards force acting on an object submerged in a fluid, is equal to the weight of the fluid it displaces
Centre of gravity
The single point through which the object’s weight can be said to act
Centre of mass
The single point through which all the mass of an object can be said to act
Couple
Two equal and opposite parallel forces that act on an object through different lines of action. It has the effect of causing rotation without translation
Density
The mass per unit volume of a material
Drag
The friction force that an object experiences when moving though a fluid
Equilibrium
For an object to be in equilibrium, both the resultant force and resultant moment acting on the object must be zero
Free-body diagram
A diagram showing all the forces acting on an object. It is a good starting point to any mechanics problem
Friction
The resistive force produced when there is relative movement between two surfaces
Newton
The unit of force
Newtons second law
The resultant force is equal to the rate of change of momentum
Normal contract force
The reaction force between an object and surface
Pressure
the force that a surface experiences per unit area. It is measured in Pascals (Pa)
Principle of Moments
For an object to be in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments
Tesnsion
The result of two forces acting on an object in opposite, outwards direction
Terminal velocity
The max velocity of an object that occurs when the resistive and driving forces acting on the object are equal to each other
triangle of forces
A method of determining the resultant forces of two forces. The two forces are joined tip to tail and the resultant force is given by the force that would complete the triangle
Upthrust
The upwards force that a fluid applies on an object
Weight
The product of an object’s mass and the gravitational field strength at its location
Give me the 6 common forces of dynamics and what they are
Weight – the gravitational force acting on an object, through its centre of mass.
Friction – the force that arises when two surfaces rub against each other.
Drag – the resistive force on an object travelling through a fluid (e.g. water or air).
Tension – the force within a stretched cable or rope.
Up-thrust – the upward buoyancy force acting on an object when it is in a fluid.
Normal Contact Force – the force arising when an object rests against another object
acting at a 90° angle to the plane of contact.
What are free body diagrams used for
Free body diagrams can be used to identify which forces act in which plane, and resolve the net
force in a particular direction.
Each force is labelled with angles and magnitudes, and by
resolving each force in to its horizontal and vertical components, the net force in a particular
direction can be calculated.
What 2 factors alter the drag force the most
The objects velocity and cross-sectional area
how is the drag force related to velocity and cross-sectional area
Drag is proportional to speed squared
Drag is proportional to cross-sectional area
How to determine terminal velocity using viscous fluid and a pulley system
- The terminal velocity of a ball bearing in viscous fluid can be determined experimentally. Take a
cylinder and fill it with a viscous liquid. Hold a ball bearing over the surface of the liquid, and
then release it from rest. At the same time, start a timer, and mark the position of the ball
bearing within the tube. When the ball bearing reaches terminal velocity, the distance it has
travelled between each time interval will be the same, and so its velocity can be determined. - To increase the accuracy of this experiment, set up a pulley system over the tube of fluid, with
the ball bearing attached on one end. On the other end, attach a strip of tape passing through a
ticker timer. The ticker timer will produce 50 dots per second on the tape, which will travel at
the same speed as the ball bearing. The distance between dots and the time can then be used to
determine terminal velocity.
How to work out the volume of an irregular object
Place the object in water
The change in volume when the object is fully submerged is equal to the volume of
the object.
When will an object sink
If the upthrust is smaller than the weight acting down
