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
Circular motion
The motion of a body along a circular path
Circular orbit
An orbit that is circular
Collision
Objects hitting eachother
Combined mass
Sum of masses involved
Conservation of energy
When energy is transformed from one type of energy into another, the total energy before and after are always the same.
Conservation of mass
Mass, including single atoms, is neither created or destroyed in a chemical reaction (not measurably anyway!)
Conservation of momentum
The total momentum of a group of a closed system remains constant in the absence of external forces
Constant speed
Speed that stays the same
Deceleration
Negative acceleration
Displacement
The change in the position of an object in a particular direction
Distance
The actual length of the path traveled by a body irrespective of the direction is called the distance traveled
Equations of motion
Set of formulas used to describe motion mathematically
Force
Forces change the state of rest or of uniform motion, the direction of motion, or the shape and size of a body
Force of gravitation
The force with which two objects attract eachother because of their masses
Free fall
The motion of a body towards the earth when no other force except weight acts on it.
Friction
The force that resists the motion of one surface relative to another with which it is in contact
Gravitational constant G
The universal gravitational constant G which appears in the equation for Newton’s law of gravitation
Gravity
Forces of attraction between two objects due to their mass
Horizontal circle
A circle that involves no gain or loss in gravitational potential energy
Impulse
Change in momentum caused by an external force
Inelastic collision
Collision where kinetic energy is not conserved (some energy is converted to sound or heat etc.)
Inertia
The property of matter that causes it to resist any change in its state of rest or of uniform motion
Kinetic energy
Energy possessed by a body by the virtue of its motion
Mass
The quantity of matter contained in a body it remains the same everywhere
Matter
Anything that occupies space and has mass
Momentum
The product of a body’s mass and velocity
Motion
Manner of how a body moves
Net force
The resulting force after all forces have been added using vector
Newton
A unit of force defined as 1 Newton force is needed to accelerate a 1kg mass 1 ms^-2
Newton’s first law of motion
A body continues in a state of rest or of uniform motion in a straight line unless it is acted upon by an external force
Newton’s law of gravitation
Force between two particles is proportional to their masses and inversely proportional to the square of the distance between them
Non Uniform Acceleration
When the velocity of a body increases by unequal intervals of time
Non Uniform Speed
When a body travels unequal distances in equal intervals of time
Non Uniform Velocity
Covers unequal distances in equal intervals of time in one direction
Covers equal distances in equal intervals but changes direction
Origin
Initial position of an object
Oscillatory motion
The to and fro motion of a body about its mean position
Pendulum
A mass (called “Bob”) tied to a piece of string
Period
For a particular vibration, the time for one complete oscillation
Pivot
Point upon which an object turns or rotates
Potential Energy
The energy of a body due to its height or the energy of a body due to its shape
Projectile
An object thrown into space either horizontally and under the action of gravity
Radius
Distance from centre of circle to edge
Range
The horizontal distance traveled by a projectile
Rectilinear Motion
The motion of a body in a straight line is called rectilinear motion
Retardation
Negative acceleration is called retardation. In retardation the velocity of a body decreases over time
Revolution
One full circle 2π
Speed
The distance traveled by a body in one unit of time is called its speed
Spring Constant
Force required to extend or compress a spring by one metre
State of motion
When a body changes its position with respect ot a fixed point
State of Rest
When a body does not change its position with respect to a fixed point
Tangential velocity
Velocity in a perpendicular direction to the centripetal force at a given instant
Tension force
Force in object that opposes them being stretched
Time of flight
The time taken by a projectile from the moment it is thrown until it touches the ground
Torque
Turning force (not applied through the centre of mass)
Unbalanced forces
When a number of forces act on a body and the resultant force is not zero
Uniform circular motion
The motion of an object in a circular path with uniform speed
Velocity
Distance traveled by a body in a particular direction per unit time
Vertical circle
Circular motion where the speed, as well as the direction of the object, is constantly changing
Weight
The force with which a body is attracted towards the center of the earth
Work
Work is done when force acting on a body moves it
