Topic 2: Forces And Moments Flashcards
(23 cards)
What is a field of force
Region of space within which a body experiences a force without being in physical contact with any other body
When object free falls what does this mean
No resistance is acting on it
What is normal contact force
Electrostatic repulsion between atoms of 2 diff obj surfaces
What is friction force
A type of resistive force that arises when two surfaces move relative to each other or are in attempted motion. Friction always opposes relative motion and is constant when an object is moving.
What is viscosity
Viscosity of a fluid is a measure of how difficult it will flow. Viscous force increases with speed (need not be proportional)
Differences between friction and viscosity
-f: b/w solid surface; v: b/w solid and fluid surfaces
-f: can exist without motion; v: only exists with motion
-f: constant with speed; v: increases with speed
What is tension
Tension is a pulling force exerted by a spring, cable, rope, rod etc on another object
What is Hooke’s law
If the limit of proportionality is not exceeded, the extension is proportional to the force/ load applied.
Hooke’s law formula
F= k x (straight line graph thru origin)
When springs are in series
-same force exerted on each spring
-total extension= sum of each extension of each spring (extension is different for each spring)
When springs are in parallel
-each spring has the same extension
-total force= sum of force on individual springs (force is different for each spring)
What is k, and what does larger k mean
k is spring constant, larger k means stiffer spring
What is buoyancy force(upthrust)
Buoyancy force is an upward force that is exerted by the fluid on a submerged or floating object due to the difference in pressures between the upper and lower surfaces of the object.
Pressure in liquid formula
Pressure in liquid= h (rho) g
What causes increase in buoyancy
-object immersed in denser medium
-larger volume of fluid displaced
What is moment of a force
The product of the force and the perpendicular distance of its line of action from the pivot or axis of rotation.
What is a couple
A pair of equal and opposite forces whose lines of action do not coincide and tends to produce rotation only.
What is a moment of a couple
Product of one of the forces and the perpendicular distance between the lines of action of the forces.
What is the centre of gravity
The cg of an obj is the point through which the entire weight of the obj may be considered to act. Point where net moment of all parts of the body is zero.
How to make an object more stable
-lower cg
-increase base area
Conditions for equilibrium
-resultant force acting on the object equals zero (translational equilibrium)
-resultant moment about any point equals zero (rotational equilibrium)
What is principle of moments
For a body to be in rotational equilibrium, the sum of all clockwise moments about any point must be equal to sum of all anticlockwise moments about the same point.
What statement to write when answering moments qns
“Taking moments about pivot ___”
