forces and motion 1 Flashcards
what is a scalar & an example of it?
has only magnitude:
speed
distance
what is a vector & what’s an example of one?
magnitude and direction:
velocity
displacement
force
equation for speed?
speed = distance / time
equation for velocity?
velocity = displacement(distance) / time
what is speed measured in?
m/s
what is acceleration?
the rate of change in velocity
what is the equation for acceleration?
acceleration = change in velocity / time
what’s on the y axis and x axis of a distance time graph?
y - distance
x - time
what does the gradient of the line in a distance time graph tell you?
the speed
what does a / line suggest in a distance time graph?
constant speed
what does a - line tell us in a distance time graph?
stationary
how do you find the gradient of a curved line?
draw a tangent to the line
what’s on the y and x axis of a velocity time graph?
y - velocity
x - time
what does the gradient of a velocity time graph tell us?
acceleration
what does / mean in a velocity time graph?
constant positive acceleration
what does a - line mean in a velocity time graph?
velocity is constant
how do you find the distance travelled in a velocity time graph?
find area under the curve
what’s the first law of motion (newton)?
a resultant force is required to change the motion of an object
what is (newtons) second law of motion?
if a resultant force acts on an object it will cause the object to accelerate
newton’s second law
the size of the resultant force is…
directly proportional to the acceleration it causes
what is the equation for force?
force (N) = mass(kg) x acceleration(m/s2)
what is acceleration messaged in?
m/s^2
what is force messaged in?
N newtons
what’s newton’s third law?
when two objects interact the forces they exert on each other are equal (magnitude) and opposite (direction)
if you are pushing a box -> 100N however the box will push back <- 100N (normal contact force)
all forces are..
vectors
what is the resultant force?
the overall force on an object
what is it called when an object has no resultant force?
equilibrium
what is terminal velocity?
when velocity remains constant
what are two things that affect air resistance?
surface area - the greater the surface area the greater number of collisions of air particles
velocity - the faster they are moving the more particles they will collide with
what do you call it when an object has changed shape?
deformed
what is it called when an object returns to its original shape after force has been applied?
elastic
what do you call it when an object stays deformed?
inelastic
what is extension?
the increase in length of a spring when it’s stretched
what is force proportional to?
force is proportional to extension
what is it called when force and extension are directly proportional?
hookes law
what is stopping distance?
minimum distance required to stop a vehicle in an emergency
what’s the equation for stopping distance?
stopping distance = thinking distance + braking distance
what is thinking distance?
how far the car travels during the driver’s reaction time
driver seeing hazard and applying the break
what are two things that affect thinking distance?
speed
-faster the further you travel
reaction time
-tired
-drunk
-drugs etc all increase reaction time
what is braking distance?
distance taken to stop under the braking force
what are some factors affecting braking distance?
speed
mass
-both increasing kinetic energy that needs to be 0 to stop
condition or quality of brakes
-if worn or faulty it won’t slow car as quick so car will travel further
traction between the car and road
-wet
-icy
tire conditions
what forces act on falling object?
weight
air resistance
what’s the equation linking mass, gravitational field strength, weight?
weight = mass x gravitational field strength
what is weight measured in?
N
newtons
what is the force that is push or pull?
applied force
what is the force in which masses are attracted to each other and the centre of the earth (weight)?
gravitational force
what is a force that acts in opposite directions?
friction
what is the force that causes drag?
air resistance or drag
what is the force that requires a stretch or compress?
spring force
what force happens in springs or cables when they are stretched?
tension
what is the force called that occurs when mass is pushed out the back of something so causing the object to move forward?
thrust
what type of force of thrust only occurs in fluids?
up-thrust
reason things float
what is the force that causes upward movement?
lift
what is the force that an attraction pulls two opposite poles together and visa versa?
magnetic
what is the force of attraction that pulls two opposite charges together?
electrostatic
where does the weight of a body act through?
centre of gravity
how can you measure the speed of a object at the bottom of the ramp?
- place a marker at the bottom of ramp
- measure a distance or 20cm from marker
- place the object at top of ramp and release
- using the marker measure the time it takes for the marker to move to the 20cm marker
- repeat this three times releasing marbles from the same position each time
- average time
- use equation speed = distance / time
- by varying the height of ramp to see how height affects the speed of the marble at the bottom
how can you measure the speed of an object while it’s going down a ramp?
- feed the ticker tape through the timer
- place the object at starting point
- attach the ticker tape to object
- start the ticker tape timer and carefully release the object (do not push)
- stop object when it reaches bottom of ramp
- remove ticker timer to analyse and repeat
how does a ticker tape timer work?
prints 50 dots per second on tape
if dots are far away object has covered more distance per time and travelled fast
how does a light gate work?
vehicle must have an interrupter to break beam of light
measures how long it takes for interrupter to pass
for example, if it takes 0.2 secs and interrupter is 10cm long you do 10cm/02s to find speed
how do you work out the gradient of distance / time graph?
gradient = rise / run
how do you work out final speed?
(final speed)^2 = (initial speed)^2 +(2 x acceleration x distance moved)
what’s normal reaction force?
when an object rests or is in contact with a solid surface, 90 degree reaction force to surface
what opposes motion?
friction
what is surface friction?
occurs between two surfaces than are in contact
- can stop an object from moving
- can oppose an object sliding
- can oppose an object rolling
what is air resistance?
opposition force of an object moving through gas (air) and drag is often used for the opposition of an object through a liquid
- reduce air resistance and drag by making an object more streamlined
- both increase with increasing speed
what would the weight of an 80kg person on the moon be?
on earth: 80kg x 10N/kg = 800N
on moon: 80kg x 1.6N/kg = 128N
moon gfs is 1/6 of earths
describe the forces that act on a falling object and what happens?
- initially no air resistance and only force acting on its weight
- as it falls it accelerates which increases its speed and hence air resistance
- causes the resultant force downwards to decreases
- acceleration decreases so not speeding up as quickly
- eventually they are equal and opposite and balance so there is no resultant force
- no acceleration and the terminal velocity is reached
practical: investigate how extension varies with applied forces for helical springs, metal wires and rubber bands
- set up your apparatus as shown in the
- measure the length of your spring without
any hanging masses. - hang a mass of 100g on the spring
- measure the new length of the spring
- calculate the extension of the spring
- repeat steps 3-5 for increasing the mass
in increments of 100g - take note of your results in the table
hookes law region is where force is directly proportional to extension - elastic
limit to proportionality X
curved - inelastic
spring breaks
what’s on the x axis of a spring/ weight graph?
spring displacement cm
what’s on the y axis of a spring/ weight graph?
weight
what is elastic behaviour?
is the ability of a material to recover original shape after the force is removed
in a spring this occurs when the force is lower than the elastic limit
loading and unloading force extension curves can be different as long as it returns to its original shape
how do you work out momentum?
momentum = mass x velocity
how do you create safety features linking momentum?
to reduce the force experienced by the passenger you need to extend the time for a passenger to stop in a collision
as force is the change in momentum divided by time
to reduce force experienced by the passengers you need to extend the time taken for a passenger to stop in a collision
MOMENTUM= MASS X VELOCITY (DISPLACEMENT/TIME)
FORCE= CHANGE IN MOMENTUM/TIME
what’s the conservation of momentum of object?
momentum before the collision = momentum after the collision
so,
momentum A before the collision + momentum B before the collision = momentum A & B after the collision moving together
what’s the relationship between force, change in momentum and time taken?
force = change in momentum / time taken
what’s newton’s third law?
when two objects interact, they apply forces to each other of equal magnitude and opposite direction
what’s the relationship of moment, force, perpendicular distance from pivot?
moment = force x perpendicular distance from the pivot
where does the weight of a body act through?
centre of gravity
use the principle of moments for a simple system of parallel forces acting in one plane:
principle of moments states that when the clockwise moments are equal to the anticlockwise moments a body will be in equilibrium
clockwise moments = anticlockwise moments
how does the upward forces on a light beam, supported at its ends, vary with the position of a heavy object placed on the beam?
when moments are taken from the right hand side as the block is a greater distance the force from the left hand pivot must be bigger to counteract it.
the opposite is true for the left hand side
what’s momentum measured in?
Kg m/s
