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NCEA Level 2 Mechanics
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Gravity
Terms in this set (62)
What is newton's first law?
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
What is newton's second law?
Fnet = ma (m≠0)
If the force on an object is zero, the acceleration of the object will be zero. This means the object will be stationary or moving at constant velocity.
What is newton's third law?
For every action there is an equal and opposite reaction.
What is torque?
Torque is the turning effect that is a result of a force being applied about a pivot.
What is the formula for torque?
T = Fd (Nm)
What is the condition for the force and the distance in the torque formula?
Force and distance must be perpendicular to each other.
How do you calculate the torque if the force applied at a certain distance is not perpendicular to the radius?
Draw force vector and calculate the perpendicular component of the force using SOHCAHTOA
What are the two conditions for equilibrium with regards to torque?
Fnet is zero and the sum of all the torques acting on the object is zero.
What is the centre of mass?
The point in an object where the object will balance when suspended or pivoted
What is momentum?
It is a quantity that involves the velocity and mass of an object.
What is the formula for momentum?
p = mv (kgms-1)
Is momentum a scalar or a vector quantity?
Vector (it has size and direction - therefore, when doing problems involving momentum always draw it)
What is impulse?
Impulse is the change in momentum caused by a force acting on an object for a period of time
(∆p = Ft) (kgms-1)
Momentum
p (kgms-1)
Speed
V (ms-1)
Distance
d (m)
Time
t (s)
Acceleration
a (ms-2)
Mass
m (but not metres)
Initial Velocity
Vi (ms-1 + direction)
Final Velocity
Vf (ms-1 + direction)
Ek/p
Kinetic/Gravitational Potential Energy
Gravity
g (9.8N)
Velocity
V (but fancier) (ms-1 + direction)
Torque
T (but fancier) (Nm)
Force
F (N)
Power
P (w)
Work
W (J)
Centripetal Acceleration
ac (but c is small)
Centripetal Acceleration Equation
ac = (v2)÷ R/r
Radius
R/r
Circumference of a circle
2πR
Velocity of object travelling in a circular motion
(2πR)÷d
What is the law of conservation of momentum?
The total momentum of two or more objects before a collision or explosion equals their total momentum after the collision.
What condition needs to be met in order for the kinematic equations to be true?
All vector values (acceleration, velocity and distance) in the equation must be in the same line.
In a distance - time graph, what is the slope?
Speed (ms-1)
In a displacement - time graph, what is the slope?
Velocity (ms-1 + direction)
In a velocity - time graph, what is the slope?
Acceleration (ms-2)
How do I find the displacement from a velocity - time graph?
Find the area under the graph
What is the result of unbalanced force?
Acceleration
What are two ways to increase the torque acting on an object?
Increase the force or increase the distance
If something is in circular motion and then released, describe the motion of the object.
The object will travel in a straight line at a tangent to the circle it was previously travelling in. This is a result of Newton's First Law - an object will move at constant velocity if Fnet = 0N. In this case the centripetal force has been removed so the object will continue at the velocity (size and direction) it had when it was released (presuming no outside forces).
What are the possible results of a resultant force not equal to zero?
Change in speed; change in direction; change in shape.
What is the difference between mass and weight?
Weight is the force that a mass exerts on earth Fg = mg; mass is the amount of mass in an object
Weight Force
Fg (but g is smaller)
Define the 'range' of a projectile.
The range is the horizontal distance that an object flies in the absence of air resistance and propulsion.
What is the trajectory of a projectile?
The angle to the horizontal at which the projectile released.
Describe a projectile at maximum height.
The vertical velocity is zero. At this point the flight time is exactly half the total flight time.
UCM
Uniform circular motion
What is the result of centripetal force in UCM?
Fc changes the direction of the velocity of the object in UCM.
What is work?
The amount of energy needed to move an object a distance (d) using a force (F). Given by the equation W = Fd
What are the units for work?
Joules
What is Power?
Power is the rate at which work is done. P = W÷t
What are the units for power?
Watts
What is kinetic energy?
The energy that a moving object possesses.
What is the law of conservation of energy?
Energy cannot be created or destroyed, it can only be changed from one form to another.
What is Ep?
Gravitational Potential Energy. Ep = mgh
What is Hooke's law?
F=kx where F is the force applied to a spring; x is the amount that the spring stretches; and k is the spring constant (rigidity) of the spring.
What is the energy in a spring?
Energy in a spring is stored as Elastic Potential Energy.
Give two examples of useful and wasteful energy changes?
Useful: Chemical to Kinetic - as in a runner using food to give energy to run; or Elastic Potential Energy to Kinetic - as in a bow and arrow. Wasteful: Chemical to heat - in running a car's engine; or Electrical to heat - in a light bulb
Convert from kmh-1 to ms-1
÷3.6
Convert from ms-1 to kmh-1
x3.6
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