Mechanics Flashcards
Distance
Distance is the total length travelled by a moving object irrespective of direction of motion.
Displacement
The displacement of an object from a reference point O is the linear distance and direction of the object from O
Speed / velocity
Speed/velocity is the rate of change of distance/displacement travelled wrt time.
Acceleration
Acceleration of an object is its rate of change of velocity wrt time.
N1L
N1L states that every body continues to be In a state of rest of to move with constant velocity unless a net force acts on it
N2L
N2L states that the rate of change of momentum of a body is proportional to the net force acting on it and occurs in the direction of the force
N3L
N3L states that that if body A exerts a force on body B, body B will exert of force of the same type that is equal in magnitude and opposite in direction on body A
*cannot say the forces cancel out
Inertia
Inertia of a body refers to its reluctance to start moving, and it’s reluctance to stop once it has begun moving m.
Mass
Mass of body is a measure of its inertia, specifying how much resistance and object exhibits to changes in velocity.
Weight
Weight of the body is the gravitational force acting on it towards the centre of the earth.
Weightlessness
No contact force acting on object (free fall)
Impulse (of a force)
Impulse (of a force) is the product of the average force acting on the object and the time interval over which it was applied.
Momentum - impulse theorem
The change in momentum of a particle during a time interval equals the impulse of the net force that acts on the particle during that interval.
(integrate F-t)
Linear momentum
Linear momentum of a body of constant mass moving with velocity is defined to be the product of mass and linear velocity.
Principle of linear momentum
PCLOM states that when bodies in a system interact, the total momentum remains constant provided no external force acts on the system.
Perfectly elastic collision
A ~ between 2 objects is one which the total KE is conserved; the relative speed of approach is equal to the relative speed of separation.
*use ke condition to solve verify if collision perfectly e
Inelastic collision
An inelastic collision between two objects is one which the total KE of system of lower after collision than before. However momentum of an isolated system is always conserved.
Head on collision
Lines of motion of both objects before and after collision are the same.
Force
The resultant force acting on an object is given by the rate of change of momentum of an object.
Field of force
Field of force is the region of space surrounding a body singing which it can exert a force on another similar body which may not be in contact with it.
- electric field is a region of space where a force acts on a stationary charge
- gravitational field is a region of space where a force acts on a mass
- magnetic field is a region of space where a force acts on a moving charge (current) or a North Pole.
Contact force
A contact force is a force between two objects which has two components. The component perpendicular to the surface is the normal force, and the component parallel to the surface is the frictional force.
Normal contact force
NCF is the net electrostatic repulsion between 2 surfaces in contact.
Friction
Friction is the force that resists relative motion between two sliding surfaces (kinetic friction), or the tendency for relative motion between 2 stationary objects (static friction).
*f =kN; dependent on area in contact
Viscous force (drag)
Viscous force is the resistive force that resists a body moving relative to a fluid.
Both viscous force and frictional force opposes relative motion but viscous force is dynamic while frictional force is static of kinetic
Tension
Tension is the force which is transmitted through a string,rope cable or wire when pulled tight by opposite ends
- medium must be taught if slack T=0
- usually medium and object inextensible
Hooke’s law
The magnitude of force F exerted by a spring on a body attached to the spring is directly proportional to the extension x of the spring from equilibrium, provided the proportional limit of the spring is not exceeded.
Elastic potential energy
EPE in a deformed material is the area under a force extension graph
Pressure
Pressure is defined as the normal force exerted per unit area.
Upthrust
Upthrust is the net upward force exerted by a fluid on a body fully or partially submerged in a fluid.
Derivation of pressure
- net horizontal force 0
- net vertical force = ro g a (height from water surface to bottom - height from water surface to top of object) aka difference between force acting on top surface and bottom surface
Archimedes principle
Archimedes principle states that when an object is totally or partially immersed in a fluid in equilibrium, the Upthrust acting on the body is equal to the weight of fluid displaced.
Principle of floatation
Principle of floatation states that a floating object in equilibrium displaced a weight of fluid (Upthrust) equal to its own weight.
Principle of moments
Principle of moments states that for a system in (rotational) equilibrium, the sum of clockwise moments about any point is equal to the anticlockwise moments about that point.
Centre of gravity
Centre of gravity of an object is the point at which the weight of the object appears to act
Moment of a force
Moment of a force about a point is the product of the magnitude of the force and the perpendicular distance of the line of action of the force to the point.
Couple
Couple is a system of forced which tends to produce a turning effect (rotation) only. A couple consists of two forces that are anti parallel, if equal magnitude and do not act along the same line of action.
Torque of a couple
Torque of couple is the product of the perpendicular distance between the lines of action of the forces and the magnitude of one of the forces.
Equilibrium
For a system in complete equilibrium, resultant force on the body must be 0 (translational equilibrium); resultant moment on the body about any axis must be 0 (rotational equilibrium)
Principle of conservation of energy
Energy can be converged from one form to another but cannot be created or destroyed
Work done by a force
The WD by a force on the body is the product of the magnitude of the force and the displacement in the direction of the force
Power
Power is the rate at which work is done
Instantaneous power
P = d WD / dt = Fv where is the instantaneous velocity
1 rad
One rad is the angle subtended at the center of the circle by an arc equal in length to the radius of the circle
Angular displacement
Angular displacement is the angle an object turns about a fixed point
Angular velocity
Angular velocity is defined as the rate of change of angular displacement wrt time
Period
Is the time taken for an object in circular motion to make one complete revolution
Frequency
Is the the number of revolutions made per unit time
