Section 4: Mechanics and Materials Flashcards
What is a couple?
A pair of coplanar forces (forces within the same plane), where the two forces are equal in magnitude but act in opposite directions.
Define centre of mass
The point at which all the weight of the object is considered to act.
What do frictional forces do?
Oppose the motion of an object, and convert kinetic energy into other forms such as heat and sound.
Define Newton’s 1st law
An object will remain at rest or move at a constant velocity unless acted on by a resultant force.
Define Newton’s 2nd law
The resultant force on an object with constant mass is directly proportional to its acceleration.
OR
The resultant force on an object is equal to its rate of change of momentum.
Define Newton’s 3rd law
For two bodies A and B:
If A exerts a force on B, then B will exert a force on A that is equal in magnitude but opposite in direction.
Define momentum
It is the product of the mass and velocity of an object.
Momentum is always conserved in an interaction where no external forces act.
Define impulse
Change in momentum, represented by FΔt.
How do you find change in momentum graphically
Find the area of a force-time graph (as it is F x Δt).
What is an elastic collision?
A collision where both momentum and kinetic energy are conserved.
What is an inelastic collision?
A collision where only momentum is conserved.
Some kinetic energy is converted into other forms such as heat, sound etc, and may be larger or smaller after the collision.
Give two examples of inelastic collisions
A collision where the objects stick together.
An explosion (since the KE after is greater than before)
Define work done
The force causing a motion multiplied by the distance travelled in the direction of the force.
Measured in joules.
Define power
The amount of energy transferred per unit time (the rate of energy transfer).
State Hooke’s law
For an object that obeys Hooke’s law, its extension is directly proportional to the force applied to it up to the limit of proportionality, provided the environmental conditions remain constant.
