vector quantities : have both magnitude and direction
examples of scalar quantities
distance
mass
temperature
density
energy
speed
time
example of vector quantities
weight
velocity
acceleration
force
displacement
Efficiency
efficiency = useful energy / total energy
efficiency= useful power / total power
Friction is a force that is always against a motion between surfaces.
Drag is a force that is always against a motion through a fluid.
Thrust is a forward force or movement given to an object due to the expulsion of an object.
Tension is a force through a material opposing an action force.
Upthrust is a force acting up due to the displacement of a fluid.
Electromagnetic force is an attraction or repulsion depending on the charge or poles.
Gravitational force, also known as weight, is a force exerted on another object due to a massive object.
Normal contact force is a reaction force or force that opposes a force applied on a surface.
Spring force is a force acting on a spring either to expand or compress.
lubricants
reduces amount of friction ( wasteful energy )
reduces amount of work done against friction
force : is a push or pull that acts on an object , causing a change in motion onto an object ( acceleration )
resultant : the sum of all vectors of the same type , resulting in a single vector acting on an object
resultant force : sum of all individual forces acting on an object , resulting in a single force causing acceleration
objects affecting each other
objects interact by exerting forces on eachother ,
these two forces ( earth and moon example ) are action reaction forces ( newton's third law pair ) . these forces are the same size , opposite direction and acting on different objects
no actual contact between moon and earth - fields ( electric and gravitational )
these are non contact forces
types of forces
contact forces
tension
friction
upthrust
types of forces
contact forces
tension
friction
upthrust
2. non contact forces
gravity
static electricity - magnetism
examples of contact forces
upthrust/lift - act upwards in air
friction (on land ) / air resistance (in air ) / drag ( in water ) - act against the direction of movement
push/pull - forces that also act in the direction of movement , generated by direct contact between objects ( not by engine power )
examples of non contact force
weight ( gravity ) - acts between objects with mass
magnetic force - magnets can attract objects from magnetic materials , can attract or repel objects , do not have to physically touch to affect each other
electric field - object charged with static electricity , has electric fields around it , can affect objects
contact forces - between two objects touching eachother
non-contact force = occurs between two objects due to a field : without touching
field : a region of space in which a object will experience a force based on one of its properties
types of fields - magnetic fields
magnetic force
non-contact
can be attractive or repulsive
types of fields - electrical fields
electrostatic force
non - contact
can be attractive / repulsive
types of field - gravitational field
gravitational force ( weight )
non - contact force
always attractive
free body diagrams
forces originate from a body
forces are acting from a single object
forces must be labeled
arrows must be proportional to size of force
weight must always act downwards , towards the centre of a massive object
the normal contact force must be perpendicular to the surface
vectors :
vectors which are perpendicular to each other are independent of one another - cannot be added or taken away
conventionally up is positive and towards the right is positive
vector diagrams
resulting ( vectors ) : representing a single force as two-forces drawing the horizontal and vertical component
reducing friction
using a lubricant : devices waste a lot f energy for various reasons due to friction between moving parts
energy is wasted in the form of : thermal and sound
thermal energy : the part around , where energy is wasted due to friction, will increase in temperature as they gain thermal energy
benefits of reducing friction :
it is the amount of friction is reduced , less energy is wasted
the efficiency of the device increases
using lubricants
a method of reducing the amount of energy wasted , due to friction is by using a lubricant
lubricant reduces the friction experienced around a turning point of a device by allowing the surface to slide smoothly over eachother
examples : door hinge , car engine ( moving pistons ) , gears
moments
a moment is the turning effect of a force around a fixed point ( called a pivot )
the size of a moment depends on two factors
size of the force applied
perpendicular distance from the pivot to the line of action of the force
moment of a force ( Nm / newton metres ) = Force ( N ) x distance perpendicular to direction of force ( m )
principle of moments
sum of clockwise moments = sum of anti-clockwise moments