Basic Concepts Flashcards
What are the SI units for :
a) time
b) distance
c) angle
d) temperature
A) second
B) Metre
C) Radian
D) Kelvin
What is another name for the rectangular co-ordinate system?
Cartesian co-ordinate system
What is the origin in the context of coordinates?
the point where all axes cross
What is formed where two planes cross each other?
a straight line
What is a plane?
a flat surface with zero thickness
What do polar coordinates systems take into account?
angle and rotation
What is displacement?
a vector quantity for distance where the “as the crow flies” distance is taken
what is velocity?
the rate of change of displacement
What is the equation for average velocity?
change in displacement/time
What is the equation for average acceleration?
Change in velocity/time
What two effects will a force have acting on an object?
change the position of the object
deform the shape of the object
What is the SI unit of Force?
Newton
What is the branch of physics that deals with forces and moments acting on objects at rest or moving at a constant velocity?
Statics
What is the first condition of static equilibrium?
the sum of all external forces acting on an object is zero
What is translational equilibrium?
equilibrium along straight lines
What is Newton’s 3rd Law?
Every action has an equal and opposite reaction
What is the SI unit of mass?
kilogram
What is weight?
W=mg
What is the equation for density?
p=mass/volume
What is gravity?
the acceleration due to the gravitational attraction between two bodies
What happens to gravity as mass increases?
Increases
what is centre of mass?
the point where all the mass of the object can be assumed to act - an average of mass distribution across an object
What is centre of gravity?
the point where the weight of the body can be assumed to act - a body only has a centre of gravity in a gravitational field
Where are the centres of mass and gravity located if a body has both?
The same point
What is pressure?
Force per unit area
What is the equation for pressure?
Pressure = force/area
What is the SI unit for pressure?
Pascal (Pa)
What kind of unit is the Pascal?
A derived SI unit
What happens to the pressure exerted when someone stands on one foot?
Pressure under the remaining foot doubles
What is the moment of a force?
the tendency of a force to produce rotation about an axis
What is another name for moment?
torque
What is the SI unit for moment?
N m (newton metres)
What is the equation for moment?
Moment = Force x Moment Arm
M = F x d
What is the second condition of static equilibrium?
the sum of all external moments acting on a body must be zero
Describe a lever system
It consists of a rigid bar that pivots about a fulcrum (which can be likened to a pivot or hinge) and is acted on by an effort force and a resistance force. The effort force and resistance force produce moments acting about the fulcrum. The length of the line that passes through the fulcrum and is perpendicular to the effort force is called the effort arm. Similarly the length of the line that passes through the fulcrum and is perpendicular to the resistance force is called the resistance arm.
What is a mechanical advantage?
When the magnitude of the effort force required to overcome a given resistance force is smaller than the magnitude of the resistance force. The effort arm is longer than the resistance arm
What is an example of a lever with mechanical advantage?
a crowbar
What is a mechanical disadvantage?
When the resistance arm is longer than the effort arm then the resistance may be moved through a relatively large distance.
How can the mechanical advantage be calculated?
MA = effort arm/resistance arm
How can the force exerted by muscles be calculated from MA and moments?
F = W x dR/dE
What is a first class lever?
give examples
Where the fulcrum is located between the effort and the resistance
scissors
see-saw
crowbar
What is a second class lever?
give examples
resistance located between the effort and the fulcrum
wheelbarrow
nutcracker
Does a second class lever work at an advantage or a disadvantage?
ALWAYS a mechanical advantage
What is a third class lever?
give examples
A third class lever has the effort located between the fulcrum and the resistance
fishing rod
tweezers
Does a third class lever work at a disadvantage or an advantage?
ALWAYS a mechanical disadvantage
