Forces New Flashcards
what does a straight diagonal line represent on a distance time graph
object is moving at a constant speed
what does a steeper line mean on a distance time graph
object is moving at a larger speed
what does increasing slope mean on distance time graphs
-increasing speed
what does decreasing slope mean on distance time graphs
-decreasing speed
how to calculate the speed from a distance time graph
-finding the gradient of the line
equation for average speed
total distance moved/total time taken
method to investigate motion of an object
- Measure out a height of 1.0 m using the tape measure or metre ruler
- Drop the object (paper cone or tennis ball) from this height, which is the distance travelled by the object
- Use the stop clock to measure how long the object takes to travel this distance
- Record the distance travelled and time taken
- Repeat steps 2-3 three times, calculating an average time taken for the object to fall a certain distance
- Repeat steps 1-4 for heights of 1.2 m, 1.4 m, 1.6 m, and 1.8 m
acceleration
the rate of change in velocity
equation for acceleration
a(m/s²) = (final velocity - initial velocity)/time
what does a straight horizontal line represent in velocity time graphs
-the object is moving with a constant velocity
what does a positive gradient in velocity time graphs mean
-object is accelerating at an constant rate
what does an increasing slope mean in velocity time graphs
-object is accelerating at an increasing rate
what does an decreasing slope mean in velocity time graphs
-object is decelerating at an increasing rate
what is uniform acceleration
constant acceleration
how to find the distance moved of a velocity time graph
find the area under the line of the graph.
how to find the acceleration of a velocity time graph
find the gradient
equation for uniform acceleration
final speed² = initial speed² +2 x acceleration x distance moved
what is reaction force
when an object rests on a surface, the surface exerts a push force on the object
what is friction
is opposes the motion of an object, causing it to slow down
what is drag
-frictional force that occurs when an object moves through a fluid
air resistance
-type of drag that only is only applied to air
thrust
-a force produced by an engine that speeds ip the motion of an object
upthrust
-when an object is fully or partially submerged in a fluid, the fluid exerts an up-ward acting push force on the object
electrostatic force
-the electrostatic force between two objects with charge
magnetic force
-the force between objects with magnetic poles
when does tension occur
-occurs in an object that is stretched
how can force affect an object
-change speed
-change direction
-change shape
what is a scalar
-quantities that have magnitude but not direction
what are vectors
quantities that have both magnitude and direction
displacement
measure of how far it is between two points in space, including the direction
velocity
measure of the displacement of an object per unit time, including the direction
what does a longer arrow mean in free body diagrams
-larger magnitude
resultant force
-single force that describes all of the force operating on a body
what are balanced forces
-the forces have combined such that they cancel each other out and no resultant force acts on the body
unbalanced forces
forces have combined such that they do not cancel out completely and there is a resultant force on the object
relationship between resultant force, mass and acceleration
f = m x a
weight (vector)
-the force experienced by an object with mass when placed in a gravitational field
mass
a measure of how much matter there is in an object
how does the gravitational field strength change depending on the characteristics of the planet
greater mass = stronger gravitation field
more massive planets(larger) have stronger gravitational field
relationship between weight, mass and gravitational field strength
w(N) = m(kg) x g(N/kg)
stopping distance
-the total distance travelled during the time it takes to stop in an emergency
stopping distance formula
stopping distance = thinking distance + braking distance
thinking distance
the distance travelled in the time it takes the driver to react to an emergency and prepare to stop
factors of thinking distance
speed of car
reaction time of driver
reaction time
-measure of how much time passes between seeing something and reacting to it
reaction time factors
tiredness
distractions
intoxication(alcohol or drugs)
braking distance
the distance travelled under the braking force in metres
terminal velocity
the fastest speed an object can reach when falling
factors affecting stopping distances
-vehicle speed
-vehicle mass
-road conditions
-driver reaction time
what is the resultant force during terminal velocity
zero
terminal velocity mark scheme
-there is a resultant force(can be weight when falling)
-it accelerates
-air resistance and friction increases as speed increases
-so acceleration decreases
-eventually air resistance + friction = driving force (forces are balanced)
-hence resultant force is zero
-object travels at a constant speed (terminal velocity)
experiment to investigate force and extension
- Align the marker to a value on the ruler with no mass added, and record this initial length of the spring / rubber band
- Add the 100 g mass hanger onto the spring / rubber band
- Record the mass (in kg) and position (in cm) from the ruler now that the spring / rubber band has extended
- Add another 100 g to the mass hanger
- Record the new mass and position from the ruler now that the spring / rubber band has extended further
- Repeat this process until all masses have been added
- Remove the masses and repeat the entire process again, until it has been carried out a total of three times, and an average length (for each mass attached) is calculated
Hooke’s law
the extension of an elastic object is directly proportional to the force applied
limit of proportionality
the point beyond which the relationship between force and extension is no longer directly proportional
elastic behaviour
the ability of material to recover its original shape after the forces causing the deformation have been removed
elastic deformation
-when the object returns to its original shape after the deforming forces are removed
inelastic deformation
when the object does not return to its original shape after the deforming force are removed
equation linking load and extension
F = kx
k = spring constant
x = extension
momentum equation
momentum = mass x velocity
p(kg m/s) = m(kg) x v(m/s)
conservation of momentum
the total momentum before an interaction is equal to the total momentum after an interaction, if no external forces are acting on the objects
how does the total momentum before a collision change after the collision
it does not change
equation relating force, change in momentum and time
force = change in momentum/time
safety features in vehicles to reduce impact of a force
increasing the contact time over which the collision occurs as force = rate of change in momentum
-seatbelts stretch slightly to increase time for passenger’s momentum to reach zero
moment
-the turning effect of a force about a pivot
equation for moment
M = F x d
d = perpendicular distance from the pivot
what direction should the force be
perpendicular to the distance from the pivot
how can you decrease the force required
increasing the distance the force is applied from the pivot
principle of moments
if an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot
how does the clockwise and anticlockwise moment differ in a balanced object
clockwise moment = anticlockwise moment
how does moving a weight away from the centre of a beam to the right supported by two blocks change the force the left support must exert
it will decrease the force on the left block and increase the force on the right block
centre of gravity
the point through which the weight of an object acts
how to find the centre of mass on symmetrical objects of uniform density
centre of gravity is located at the point of intersection of lines of symmetry
how to find the centre of gravity on a irregular object
- suspend the irregular shape from a pivot and allow it to settle
- a plumb line is then held next to the pivot and a pencil is used to draw a vertical line from the pivot
- repeat this process, suspending the shape from two additional points
- the centre of mass is located at the point where all three lines cross
