forces and energy Flashcards
Origin or reference point
the initial position of an object
distance
the difference between two position measurements
how is distance represented?
d
time
the difference between two time measurements
how is time represented?
t
speed
the rate of change of position
about average speed:
Average speed does not take into consideration the path or direction the object traveled to reach its destination
written formula for average speed:
Average speed = distance an object travels (including curved lines)/time taken for the journey.
what are the three simple equations for finding variables concerning speed?
s=d/t, t=d/s, d=sxt
position
the place relevant to an agreed origin
what is a scalar quantity?
a quantity that just has magnitude (size). They have no direction such as speed, distance and time
what is a vector quantity?
a quantity which has magnitude and direction, including velocity and force
what is a position time graph?
show the movement of an object from it’s origin. as time progresses, the object will either move further away from the point of origin, stop and not move or return closer to the point of origin.
acceleration
the term used when the rate of speed of an object is increasing- m/s^2
deceleration
the term used when the rate of speed of an object is decreasing
slope of a line on a graph
- the “steepness” of a line is called its slope
- the rise is equal to the height of the triangle
- the run is equal to the length along the base of the triangle
slope of position-time graphs
- the slope is the gradient
gradient = rise/run, which equals speed
Position time graphs and speed
- a steeper line on a position vs. time graph means a faster speed
- a line with zero slope means the object is not moving
about a velocity (speed)-time graph?
- a straight sloped line with positive slope means the object is accelerating or speeding up at a constant rate.
- a horizontal line means the object is travelling at a constant speed
- A straight sloped line with negative slope means the object is decelerating at a constant rate.
- The slope of the line shows how fast the object is acelerating or decelerating
average speed:
a single value for speed that best represents the motion of an object; speed change divided by time interval.
SI units
a set of units agreed on by all nations, meters and seconds
Car safety systems:
- all car safety systems TRANSFER ENERGY so that it has a less dangerous effect on people
- car safety systems are designed to slow the rate of energy transfer.
crumple zones
a protective part of a vehicle that is designed to buckle in a collision so that energy in an accident is slowed and the car slows down over a longer distance.
Force= energy transferred (N) / distance (d)
Work
when work is done energy is transferred AND when energy is transferred work is done.
WORK DONE=ENERGY TRANSFERRED
Mechanical work:
Mechanical work is done when a force (f) is applied over a DISTANCE (d)
WORK=FORCE X DISTANCE
W=FxD
Work=joules
Force=Newtons
distance=meters
Seat belts:
holds the occupant to their seat so their motion forward is stopped
Air bags:
increase the stopping distance of a persons head and protects it from hard structures.
conversion of kilometers to meters
(length in meters) = 1000 x (length in kilometers)
conversion of meters to kilometers
(length in kilometers) = (length in kilometers) / 1000
conversion of minutes to seconds
(time in seconds) = 60 x (time in minutes)
conversion of seconds to minutes:
(time in minutes) = (time in seconds) / 60
conversion of hours to seconds:
(time in seconds) = 3600 x (time in hours)
conversion of seconds to hours:
(Time in hours) = (time in seconds) / 3600
conversion of m/s to km/h
(speed in km/h) = 3.6 x (speed in m/s)
conversion of km/h to m/s
(speed in m/s) = (speed in km/h) / 3.6
finding speed change:
speed change = final speed - starting speed
average acceleration
a single value for acceleration that best represents how the speed of an object changes.
average speed = speed change / time taken (t)
reaction time:
the time between observing a need to act and acting
reacting to an emergency:
the slower the car travels, the greater the chance they have of stopping before tragedy results
stopping time:
the total time to come to a stop after observing the need to react
braking time:
the time over which a negative aceleration applies
formula for stopping time:
stopping time = reaction time + braking time
what are the four main factors involved in braking?
- visibility
- the driver
- the car
- road surface
stopping distance:
the total distance to come to a stop after observing the need to react
stopping distance = reaction distance + braking distance]
braking distance:
the distance while applying the brakes until coming to a stop
reaction distance:
the distance travelled before responding to the need to act
Force
F
formula for forcing
F (by agent on receiver)
finding acceleration
a = F (net) / m
a= speed F(net)= Newtons m= weight
Newton’s first law:
objects stay still or travel in straight lines at constant speed unless a net force acts to cause:
- a gain in speed (positive acceleration)
- a loss of speed (deceleration)
- a change in direction
- a change in speed and direction simultaneously
Newton’s second law:
We can calculate the effect of force and mass on the acceleration of objects by the algebraic relation:
a = F(net) / m
Newton’s third law:
forces act in pairs: F(by agent on receiver) and F(by receiver on agent, They;
- are the same size
- are opposite in direction
- act on different objects
You cannot form a net force with these two together!
