Mechanics and Materials Flashcards
Vectors and scalars
Vectors have both a magnitude and a direction, compared to
scalar quantities which only have a magnitude
Newtons’ law
Newton’s first law of motion states that a body will continue in its state of rest or uniform motion in a straight line unless an external resultant force acts on it.
Newton’s second law states that the rate of change of momentum of a body is proportional to the resultant force acting on it and the change takes place in the direction of the force.
Newton’s third law states that: If body A exerts a force on body B, then body B exerts a force of equal magnitude but in the opposite direction on body A.
Conservation of momentum
Conservation of momentum states that the total momentum of a system of objects before an event remains constant after provided no resultant external force acts on the system
Hooke’s Law
Hooke’s Law states that within the limit of proportionality, the extension produced in a material is directly proportional to the load applied.
The principle of moments
Equilibrium
The principle of moments states that the sum of the clockwise moment is equal to the sum of the anticlockwise moment for a body in equilibrium
An object is in equilibrium if there is no resultant force and no resultant moment
A couple
A couple is a pair of forces, equal in magnitude but opposite in direction, whose lines of motion do not coincide.
Friction
Drag
Lift
Terminal Velocity
Friction is a force that opposes motion when moving on a solid.
Drag is a force that opposes motion in a fluid. It usually increases with speed.
Lift is an upward force created on an object as it moves through a fluid
due to the shape of an object.
Terminal Velocity happens when
frictional forces equal the driving force,
causing equilibrium and zero acceleration.
In a closed system, an inelastic collision and an elastic collision
In a closed system, momentum is conserved. This means that the product of
velocity and mass must be the same before and after. This occurs in both collisions and explosions.
In an inelastic collision, kinetic energy is not conserved. This means we can work out the change in kinetic energy and hence how much energy dissipated into other forms.
In an elastic collision kinetic energy is conserved. This means we can work out the kinetic energy before and after given smaller pieces of information.
Elastic and Plastic Deformation
Elastic Deformation: Material returns to original shape and has no permanent extension. Energy is stored as elastic strain energy e.g. an elastic band
Plastic Deformation: Material is permanently stretched because the atoms have physically moved relative to one another. Energy is used to deform it e.g polythene
Tensile Stress and Tensile Strain
Tensile Stress is the force applied per unit cross-sectional area, measured in Pa or Nm⁻²
Tensile Strain is the extension per unit original length and has no unit
Centre of mass
the point on an object through which the entire weight of the object may be considered to act.
Elastic Limit
The point where the maximum stress that a piece of material can withstand without being permanently deformed
Speed
The rate of change of distance traveled with respect to time
Velocity
The rate of change of its displacement with respect to time
Acceleration
Acceleration of an object is the rate of change of its velocity with respect to time
