Section 4 - Mechanics Flashcards
Scalars vs Vectors
Scalars have only magnitude
Vectors have both magnitude and direction
Examples of Scalars
Mass, temperature, time, length, distance, speed, energy
Examples of Vectors
Displacement, velocity, force, acceleration, momentum
Two methods of adding vectors
Scale drawings, Trig
Adding vectors using scale drawings
Draw the vectors tail to tail and then connect the ends with the resultant vector
Measure the magnitude and angle (from the north vector)
Adding vectors using trig
Vectors at right angles can be used to form a triangle, use trignomenty to find the resultant magnitude and angle
Trig
SOH CAH TOA
Resolving vectors
Using trignometry to split a vector into vertical and horizontal components
What should free body diagrams include
The diagram should only include all the forces that act ON the object
If a body is in equilibrium…
The forces acting on it are balanced in each direction
Three coplanar forces in equilibrium
You can draw a closed loop triangle
Moment def
A moment is the turning effect of a force
Components of a lever
Effort, Load and Pivot
Principle of Moments
The principle of moment states that for a body to be in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point
Moment formula
M=f*d
A couple of forces
A pair of coplanar forces of equal size which act parallel to each other but in opposite direction
Moment of a couple
size of one force * perpendicular distance between the line of action of the forces
Weight def
The force acting on an object due to its mass and the gravitational field
Weight formula
Mass*g
Centre of mass def
A single point though which the mass of the object acts
Finding the centre of mass of a regular polygon
Lines of symmetry
Steps for finding the centre of mass of an irregular object
1) Hang the object freely from one point
2) Draw vertical lines downwards from the point of suspension (using a plumb blob)
3) Repeat by hanging from different points
4) The centre of mass is the intersection of points
Stability of an object
If the centre of mass lies above the base of the object, it will be stable
How can the stability of an object be increased
Using a lower centre of mass and a wide base
Speed def
How fast something is moving, regardless of direction
Displacement def
How far an objects travelled from its starting point in a given direction
Velocity def
The rate of change of an objects displacement
Acceleration def
The rate of change of an objects velocity
Velocity f
s/t
Acceleration f
v/t
Area under a velocity time graph
displacement
Gradient of a displacement time graph
Velocity
Gradient of a velocity time graph
Acceleration
Area under a acceleration graph
Change in velocity
Drawing displacement time graphs using a data logger
Ultrasound position detector
Data logger
SUVAT equations
INSERT PIC
Experiment to calculate g
NL1
The velocity of an object will not change unless a resultant force acts on it
NL2
Acceleration is proportional to force
NL2 formula
f = ma
NL3
If object A EXERTS a FORCE on object B, then object B exerts AN EQUAL AND OPPOSITE FORCE on object A
Friction def
A force that opposes motion
Two types of friction
Fluid Friction and Dry Friction
Factors that influence fluid friction
Fluid Viscocity or thickness
Speed (Friction increases as speed increases)
Shape of object
3 main points to remember about friction [3]
1) They always act in the opposite direction to the motion of the object
2) They can never speed things up or start something moving
3) They convert kinetic energy into heat and sound
Lift definition
The upward force on an object moving through a fluid
How lift works
The shape of an object causes the fluid flowing over it to change direction
Three stages of reaching terminal speed
1) Object accelerates from rest with a driving force
2) As speed increases friction increases
3) Eventually driving force and friction are equal so there is no acceleration
Factors that affect an objects terminal speed
Increasing the driving force
Reducing the frictional force
Terminal speed during free fall
Momentum formula
p = mv
Conservation of momentum
The total momentum before two objects collide is equal to the momentum after the collision, assuming no external forces act on it
Elastic Collision
Inelastic Collision
Principle of impulse in words
Principle of impulse formula
Ft = mv-mu
impulse = change in momentum
Reducing force in a collision
Increase the time taken for the collision, reducing the force
Work done
The transfer of energy, energy change
Work done formula
W = Fs
Assumption, formula of work done
Assumes that the direction of force is the same as the direction of movement
Joule
One newton moving an object by a distance of one metre
Area under a force-displacement graph
Work Done
Power def
The rate of doing work
Power Formulae
Work done / time (P = W/t)
Force*Velocity (P = Fv)
Watt
1 joule per second
Principle of conservation of energy
Energy can not be created or destroyed, it con only be transferred from one form to another but the total amount of energy in a closed system will not change
Efficiency f
useful output power/input power
KE f
1/2 m v^2
GPE f
mgh
Elastic strain f
1/2 k l^2
