Moments Flashcards
What is weight?
The downward force a mass has due to gravity
What is weight measured in?
Newtons
What is mass?
The amount of matter an object is made of.
What is mass measured in?
Grams (g) or kilograms (kg)
What is w = m x g
Weight = mass x gravitational field strength
What is a pivot?
The point of which a lever can rotate around when a moment is present
What is a lever?
A rigid body which revolves around the pivot
What is a moment?
The turning effect of a force
What is the equation to calculate moments?
Moment = force x perpendicular distance
What is a moment measured in?
Newton meters (Nm)
What is perpendicular distance measured in?
Meters (m) or centimetres (cm)
What is effort?
The force exerted on the lever
What is load?
The force that is being moved
define elastic limit
The point beyond which materials that are elastic no longer obey hooke’s law
Define plastic deformation
The permanent deformation when an unloaded material that has previously been stretched or squashed doesn’t return to its original shape
Define contact force
Any force that can only be exerted when objects are touching
Define non-contact force
Any force that can be exerted without objects touching
What is Center of mass?
The point from which the weight of an object appears to act from
What is hooke’s law?
That for a spring,force is directly proportional to extension up until the elastic limit
What is directly proportional?
When one variable increases, the rate that the other increases by remains constant
What is extension?
Extension of elastic material = original length - new ( stretched length)
What is the equation for Hooke’s law?
F = k x e ( force = spring constant x extension)
What is force measured in?
Newtons N
What is elastic deformation?
The deformation whereby an elastic material that has been stretched returns to its original Shape afterwards
How do you find the center of Mass on a regular object?
Find two lines of symmetry and the Center where the two lines meet is the Center of mass.
How do you find the Center of mass on an irregular object?
Punch a hole in 3 places at random then hang a string from them one at a time and attach a plumb line from each one and then draw a line whilst holding the plumb line in place. Do this for all the holes and then find the place where are the lines meet and that will be the center of mass
Is elastic deformation permanent or temporary?
Temporary
Is plastic deformation permanent or temporary?
Permanent
On a deformation graph, what axis are the force and extension on?
Force on y axis
Extension on x axis
Does elastic deformation obey hooke’s law?
Yes, as both force applied to elastic material and extension are directly proportional.
Does plastic deformation obey hooke’s law?
No, as the elastic material has passed it’s elastic limit, so when a force is applied, the object will stretch, but not return to its original shape.
What is the yielding point?
The points that indicates the end of elastic behaviour in an object and the start of plastic behaviour
Something is in equilibrium when….
Total Anti-clockwise moment = total clockwise moment
Why would a bus with the centre of mass outside its base topple in comparison to a bus with the centre of mass in its base?
The bus with the centre of mass outside its base would topple over as the weight creates a destabilising anti-clockwise moment about the centre of mass so it falls. In the bus with the centre of mass inside its base, the weight of the bus creates a stabilising clockwise moment about the centre of mass so it stays upright.
How is it beneficial for the load to be closer to the pivot?
The weight of the load acts from the CoM of the load, creating anti-clockwise moment about pivot. Closer the load to pivot, the smaller the moment. In order for load to be lifted, the boulder’s moment must be equal to the effort to lift the load. So, smaller moment from weight of load = smaller clockwise moment needed to lift it. Therefore, moment and so effort could be reduced to lift the load by moving the load closer to pivot or by increasing the distance effort is applied from.