Mechanics -Terms and definitions Flashcards
Gravitational Acceleration
9.8m/s/s
Newton’s Second Law of Motion
If acceleration and velocity are in the same direction, the object is accelerating.
If acceleration and velocity are in opposite directions, the object is decelerating.
Where there is an acceleration we use kinematic equations.
Elastic and Inelastic Collisions
During a collision, if there is NO loss of kinetic energy, we call it ELASTIC collision.
During a collision, if there IS loss of kinetic energy, we call it INELASTIC collision.
(There will always be some lost due to friction, but if it’s a not much then it’s inelastic)
Ek=(1/2)mv^2
Circular motion equations (5)
Fc=mac
Fc = centripetal force = Newtons = N
m = mass = kg
ac = centripetal acceleration = m/s/s
v=(2πr)/T =2πrF v = velocity = m/s π = pie r = radius T = period = unit: S F = frequency = unit: S^-1 or Hertz (Hz)
Fc=(mv^2)/r
c=2πr
c = circumfrence
π = pie
r = radius
ac=(v^2)/r
Energy Equations (5)
P=W/t W=F/d Ek=(1/2)mv^2 W=Pt Ep=mgΔh
Power
The rate at which energy is transformed (how fast it's transformed). P=W/t or P=ΔE/t P = Power -J/s or Watts (W) W = Work (J) ΔE = change in energy (J) t = time (s)
Projectile motion horizontal
In the horizontal direction, there is no force acting on the object, so the horizontal velocity will stay the same. (No acceleration).
Rounding
To the least accurate amount of significant figures that is given in the question.
Because the end result’s accuracy can’t be more accurate than the data given itself.
(Round at the end of the question only)
Equilibrium
All forces are balanced, no linear acceleration.
Clockwise torque equals to anticlockwise torque, no angular acceleration.
Torque
Def: Torque is the turning effect of a force around a pivot point.
Torque is sometimes called ‘moment’, or ‘moment of force’.
symbol: T
Momentum
The quantity of motion of a moving body, measured as a product of its mass and velocity.
Used in EXPLOSIONs and COLLISIONs.
“Moving objects resist being stopped, a quality which we call their inertia. We experience a force when struck by a moving object created by a change in momentum.”
Momentum is a vector quantity, it has both size and direction. The direction of momentum is the same as the velocity.
Elastical Potential Energy
Stretched out string, once you let it go it will contract similar to dropping a ball w gravitational Ep.
Ep=(1/2)kx^2
Ep = Elastic Potential Energy (J)
k = spring constant (N/m)
x = extension (m)
Conservation of Momentum
The momentum of a system stays the same if there’s no external force acting on it.
This is used in collisions and explosions.
Circular Motion
“Newton’s first law states that a body will continue at a constant velocity in a straight line unless it is acted on by an external force. The velocity of the spinning object is constantly changing so there must be an external force acting upon it -the centripetal force. Remove the centripetal force and the object flies off at a tangent.”
An object rotates around a fixed point with a constant speed and radius.
The direction of the velocity is TANGENTAL (In tangent to the circle)
Even though the SPEED of the object does not change, the direction is constantly changing thus the velocity is constantly changing.
Projectile motion vertical
In the vertical direction, the only force that is acting is gravity going down. It is under constant acceleration at 9.8m/s/s
ac
centripetal acceleration
Period (T)
def: The time that it takes for one revolution (one circle) to occur.
Unit: S
Projectile def
A projectile is any object that moves through the air without its own source of power, only under the influence of gravity (air resistance is ignored).
Impulse
Change of momentum is caused by a force over a period of time.
ΔP->=Ft
ΔP = kgm/s (the arrow shows the direction of the net impulse).
F = N
t = s
Kinematic Equations
Vf=Vi+at
d=Vit+1/2at^2
Vf^2=Vi^2+2ad
d=((Vi+Vf)/2)t
Vi = initial velocity (m/s) Vf = final velocity (m/s) t = time (s) a = acceleration (ms^-2) d = distance (m)
Spring Constant
Represents the stiffness of the spring (the bigger the spring constant the stiffer the spring)
F=kx or F=-kx F = Force (N) k = Spring constant (N/m) x = Extension (m) (-) = Restoring force in the spring -essentially the force opposing the extension (downwards) force. Don't often need to use.
Conservation of Energy
Energy cannot be created or destroyed
In a system that does not undergo any force from outside the system, the amount of energy is constant, irrespective of its changes in form.
Fc
Centripetal force
Torque Calculations
T=Fd
T = Torque = Newtons per meter = N.m
F = Force = Newtons = N
d = perpendicular distance (from pivot pt.) = meters = m
Tac=Tc
Tac = Sum of Torque anticlockwise
Tc = Sum of Torque clockwise
Verticle Motion under Gravity
When an object is under free-fall, provided air resistance can be ignored, its acceleration is due to gravity.
Kinetic Energy
Is the energy an object has because of its movement. As an object speeds up it gains kinetic energy, as it slows down it loses it.
Ek=(1/2)mv^2
Newton’s Third Law of Motion
Every acting force will have an equal and opposite reaction force.
Newton’s First Law of Motion
If all the forces acting upon an object are balanced, then the object will either stay stationary or travel at a constant speed/velocity.
d=vt
(Acceleration = 0)
If the forces acting upon an object are NOT balanced, then the object will have an acceleration. The direction of the acceleration will be the same as the net force.
a=F/m or F=ma
Frequency (F)
def: The number of revolutions that can happen in 1 second.
Unit: S^-1 or Hertz (Hz)
Gravitational Energy
When an object is able to gain kinetic energy in the future on account of its position, being raised above the ground.
ΔEp=mgΔh
Momentum equations
P=mv
P = momentum = kg.m/s
m = mass = kg
v = velocity = m/s
Ptotal-> = Pa-> + Pb->
Work
If a force acting on an object has moved the object in the direction of the force for a distance, then we say the force has DONE WORK.
Work done = energy transformed
thus
when energy is transformed, there must be a force doing work.
W=Fd
Accelerate vs acceleration
Accelerate: When something changes its velocity
Acceleration: The rate of change of velocity of a moving object. Can result from a change in speed and/or a change in direction
Acceleration due to gravity
On surface of earth, value is 9.8ms^-2
Increases nearer the poles, decreases with altitude and depth inside the earth
Average velocity
Total displacement divided by the total time taken
Axis
The imaginary line about which a planet or other object rotates
Balanced forces
When a number of forces act on a body, and the resultant force is zero
Centripetal force
Force required to keep an object moving in a circle
Change in momentum
Momentum after minus momentum before
Change in velocity
Velocity after minus velocity before
