forces and motion Flashcards
what do distance-time graphs tell you
how far something has travelled
what does the gradient on distance-time graphs tell you
the speed of the object (steeper the gradient, the faster the object)
what do the flat sections of a distance-time graphs tell you
it is stationary
what does a steeper line on a distance-time graph tell you
it’s going faster
what does a curve represent on a distance-time graph
acceleration/deceleration
what does a curve getting steeper mean on a distance-time graph
it’s speeding up
what does a levelling off curve mean on a distance-time graph
it’s slowing down
equation linking average speed, distance and time
average speed = distance/time
speed (m/s) =
distance (m) / time (s)
practical: investigate motion of everyday objects such as toy cars or tennis balls
METHOD 1 - USING A STOPWATCH
1) place a fiducial marker at the bottom of a ramp. with a ruler measure a distance of 50cm from this marker and place a second fiducial marker
2) place the marble at the top of the ramp and release without applying any force
3) using a stopwatch measure the amount of time it takes for the marble to go from marker to marker
4) repeat 3x and release marble from same position each time
5) calculate average time
6) speed = distance/time
7) increase height of ramp by 5cm and repeat steps
METHOD 2 - USING TICKER TAPE
1) place the trolley at the starting position
2) tape the ticker tape to the back of the trolley using masking tape and carefully feed the ticker tape through the timer
3) start the ticker tape time and carefully release the trolley without applying any force
4) the further apart the dots, the faster its travelled
5) repeat 3x and find average
what is the relationship between acceleration, change in velocity and time taken
acceleration = change in velocity/time taken
acceleration =
change in velocity / time taken
what does the gradient show you on a velocity-time graph
acceleration
what do flat sections represent on a velocity-time graph
steady speed
what do uphill section ( / ) tell you on a velocity-time graph
acceleration
what do downhill sections ( \ ) tell you on a velocity-time graph
deceleration
how do you work out the distance travelled from a velocity-time graph
area under graph
what does a curve mean on a velocity-time graph
changing acceleration (increasing/decreasing)
how do you determine acceleration from a velocity-time graph
use the gradient
rise/run
state the equation linking weight, mass and gravitational field strength
weight = mass x gravitational field strength
weight (N) =
mass (kg) x gravitational field strength (N/kg)
different types of forces:
- GRAVITY or WEIGHT - acts straight downwards
- REACTION FORCE - acts perpendicular to a surface and away from it
- ELECTROSTATIC FORCE between two charged objects
- THRUST - like push/pull
- DRAG or AIR RESISTANCE or FRICTION - slowing the thing down
- LIFT - eg. due to an airplane wing
- TENSION - in a rope or cable
investigate the motion of a toy car on a ramp:
- make sure the car starts from the same spot each time by marking a line on the ramp
- measure the distance between each light gate
- let go of the car just before the light gate so it starts to roll down the slope
- when the car passes through each light gate, a beam of light is broken and a time is recorded by a data logging device
- repeat 3x and find average
- speed = distance/time
state the equation linking force, mass and acceleration
force = mass x acceleration
force =
mass x acceleration
vectors have…
direction and magnitude
scalars have…
magnitude
is force a vector or scalar quantity
vector
examples of vector quantities
force, acceleration, velocity, momentum
examples of scalar quantities
mass, temperature, time, length
how do moving objects reach a terminal velocity
1) when an object first starts to fall, it has much more force accelerating it than resistance slowing it down
2) as the velocity increases, the resistance increases
3) the resistance gradually reduces the acceleration until the resistance is equal to the acceleration
-> the object can’t accelerate any more and has reacher its terminal velocity
what does Hooke’s law say
extension is proportional to force
extension =
new length - original length
what is the initial linear region of a force-extension graph associated with
Hooke’s law
what is elastic behaviour
the ability of a material to recover its original shape after the forces causing deformation have been removed
investigate how extension varies with applied for force
1) measure the length of the spring/elastic band with no mass applied
2) add one mass at a time and allow the spring/elastic band to come to rest, then measure the new length of the spring/elastic band
-> the extension is the change in length from the original length
-> repeat this process until you have enough measurements
3) repeat 3x and find average
4) plot results on graph with force on y-axis and total extension of x-axis
investigate how extension varies with applied for force
1) measure the length of the spring/elastic band with no mass applied
2) add one mass at a time and allow the spring/elastic band to come to rest, then measure the new length of the spring/elastic band
-> the extension is the change in length from the original length
-> repeat this process until you have enough measurements
3) repeat 3x and find average
4) plot results on graph with force on y-axis and total extension of x-axis
when does Hooke’s law stop working and how is this shown on a graph
stops working when force is great enough
shown when the graph starts to curve
stopping distance =
thinking distance + breaking distance
factors affecting thinking distance
speed, reaction time
factors affecting braking distance
speed, mass of vehicle, quality of brakes, grip on road
factors affecting stopping distance
speed, mass, road condition, reaction time
