Module 3 | Forces and Motion | Equations

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Average Speed
Speed = Total distance travelled / Time taken
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Velocity
Velocity = Change in displacement / Time taken
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Acceleration
Acceleration = Change in velocity / Time taken
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SUVAT equation without displacement (BOOKLET)
v = u + at
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SUVAT equation without final velocity (BOOKLET)
s = ut + 1/2 * at^2
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SUVAT equation without acceleration (BOOKLET)
s = 1/2 * (u + v)t
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SUVAT equation without time (BOOKLET)
v^2 = u^2 + 2as
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Value of g (Positive resultant is upwards.)
-9.81
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Projectiles
Horizontal velocity stays constant. Vertical velocity changes by a rate of g.
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Projectile projected at an angle
Horizontal velocity is constant at vCosθ. Vertical velocity is vSinθ.
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Resultant force in terms of mass and acceleration
Resultant force F acting on an object of mass m will produce acceleration a. F = ma.
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Weight in free-fall
An object in free fall on the surface of the Earth has acceleration g . The weight W of the object is equal to the product of the mass m and the acceleration of free fall g. W = mg.
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Factors affecting drag
Speed of the object (>Speed = >Drag); Cross-sectional area at right angles to the direction of tavel (>Area = >Drag); Viscosity of fluid.
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Just before falling
Speed = 0; Drag = 0; Resultant force = weight; Acceleration = g;
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During the flight
Speed > 0; Drag > 0; Resultant force F = mg - drag; Acceleration = (mg-drag)/m
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Terminal velocity
Speed = constant; Drag = weight; Resultant force = 0; Acceleration = 0
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Moment of a force
The moment of the force is the product of the force applied and the perpendicular distance of the line of action from the pivot. Moment = Fx. Can be clockwise (-) or anticlockwise (+). Units Nm.
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Principle of moments
(WHEN EQUILIBRIUM) Sum of clockwise moments about the pivot = sum of anticlockwise moments about the pivot.
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Torque of a couple
The torque of a couple is the product of one of the forces and the perpendicular separation between the forces. Torque = Fd.
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Density
Density = Mass / Volume.
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Pressure
Pressure = Force / Cross-sectional area.
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Pressure from water
Pressure = Depth * Density * Gravitational field strength.
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Archimedes' principle
The upthrust exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces.
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Work done
Work done = Force * Distance moved in the direction of the force. Work done = Energy transferred.
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Kinetic Energy
Ek = 1/2 * mv^2 = 1/2 * mass * velocity^2.
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Gravitational Potential Energy
Ep = mgh = mass * gravititational field strength * height.
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Kinetic Energy and GPE changes (Energy transferred between)
v^2 = 2gh.
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Power
Power = Work done / time OR Power = Energy transferred / time.
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Efficiency
Efficiency = ( Useful energy output / Total energy input ) * 100 [Cannot be > 100%]]
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Hooke's Law
F = kx
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Elastic Potential Energy
E = 1/2 Fx OR E = 1/2 kx^2
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Stress
Stress = Force / Cross-sectional area
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Strain
Strain = Extension / Original length
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Young modulus
Young modulus = Stress / Strain
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Newton's first law of motion
An object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force.
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Newton's third law of motion
When two objects interact, they exert equal and opposite forces on eachother. Remember; The forces cannot act on a single point; The forces are in opposite directions; The forces have the same magnitude; Both forces must be of the same type.
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Momentum
Momentum = Mass * Velocity
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Newton's second law of motion
The resultant force acting on an object is directly proportional to the rate of change of its momentum, as is in the same direction. Resultant force = k * Rate of change of momentum.
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Deriving F = ma from Newton's second law?
F = Change in momentum / Change in time = mv - mu / t = m ( v - u / t ) = ma
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Impulse
Impulse = mv - mu
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Other cards in this set

Card 2

Front

Velocity = Change in displacement / Time taken

Back

Velocity

Card 3

Front

Acceleration = Change in velocity / Time taken

Back

Preview of the back of card 3

Card 4

Front

v = u + at

Back

Preview of the back of card 4

Card 5

Front

s = ut + 1/2 * at^2

Back

Preview of the back of card 5
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