2.3 Forces In Action Flashcards
What is the difference between elastic and plastic bodies?
Elastic - Objects that return to original shape after the deforming force is removed.
Plastic - Objects that do no return to original shape when deforming force is removed.
What is plastic deformation, elastic limit and limit of proportionality?
If force applied on a spring is too great it suffers plastic deformation so no return to orignal shape.
A spring abides Hooke’s law till limit of proportionality is exceeded.
Elastic limit is the point which a body is permanently deformed when the deforming force is removed.
What is Hooke’s law?
Force Applied = Spring Constant * Extension
Spring Constant is gradient of force/extension graph. A diagonal straight line follows Hooke’s Law till the limit of proportionality is exceeded.
What is elastic potential energy?
The energy stored by an elastic body that has been stretched. The greater the extension, the stiffer it is.
Work Done = Mass * Displacement
Energy is transferred from EPE to KE.
EPE = 1/2 * k * e^2
How does EPE link to work done and Hooke’s law?
Work done is done when energy from the elastic potential energy store to kinetic energy.
EPE is the area triangle underneath force/extension graph. This is 1/2 * total extension (x axis) * total force (y axis)
Force = KE
Therefore EPE = 1/2 * e * e * k
What is a force field?
A field is a regions of space within a body experiences a force. Gravity exist around mass, magnetism around magnets, electrostatics around charge. Fields do not always exert the same force.
What is mass, gravity and weight?
Mass is the amount of matter. Weight is the downwards force acted on a body. Gravity is a force field and an acceleration (F=MA).
Weight (F) = Mass (M) * Gravitational Strength (A)
What is gravitational potential energy?
GPE is the energy stored in a body when its height is raised in a gravitational field. Force must be applied to counter weight thus work is done where the final energy is GPE.
GPE(W) = Mass * Gravity Strength(F) * Height(D)
What is a moment? How do you calculate the moment?
A turning force and effect creates a moment. The moment depends on the size of the force and the distance from the pivot point at which the force acts.
Moment of a force (Nm) = Force (N) X Distance (m)
What is the principle of moments?
An object is balanced if the anticlockwise moments are equal to the clockwise moments about the pivot.
How do levers transmit force?
Load, Effort
A lever is a force multiplier and transmits force by rotating about a pivot. The effort is the force exerted on the lever and the load is the force that the lever exerts on the load. If the pivot is close tot he load then a small effort is needed to lift it.
What is mechanical advantage?
Mechanical Advantage is the ratio of load to effort.
Mechanical Advantage = Load /// Effort
How do gears transmit force?
If a smaller cog rotates with a certain force, it makes a larger cog rotate. The bigger cog will then exert a bigger force, but will not move so far. In both cogs, the force X distance is the same.
What is a hydraulic machine?
It is almost impossible to compress liquids and so a machine that uses this property to transmit a force with a liquid is called a hydraulic machine. It is a force multiplier.
