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Flashcards in Motion 1 Deck (24):

what is an objects weight

mass x gravitational field strength


what is tension

a force exerted inwards on the ends of objects like string to oppose extension


what is upthrust

an upward force on an object exerted by the fluid it is partially/fully submerged in


what is frction

a force opposing motion


what is a normal contact force

a force exerted on an object by the surface it is on, perpendicular to the surface it is on


what is drag

the frictional force experienced when travelling through a fluid


what factors affect drag when travelling in air

-velocity (drag ∝ speed²)
-surface area facing the direction of travel
-density of the air


what is
-thinking distance
-breaking distance
-stopping distance

-the distance traveled from seeing the obstacle to engaging the breaks
-the distance traveled from the brakes being applied to coming to a stop
-thinking distance + braking distance


what is the relationship between
-speed and thinking distance
-speed and braking distance
and why

-thinking distance ∝ speed, the faster you go the further you will travel while reacting to the obstacle
-braking distance ∝ speed², to stop the brakes must dissipate all of the car's kinetic energy, which = 0.5mv², so as speed doubles, kinetic energy increases by a factor of 4, so it takes 4 times as long to dissipate all of the energy


describe an object's acceleration as it reaches terminal velocity, in terms of forces

-just after falling, net force = weight as there is no drag acting on it, so a = 9.81
-between jumping and reaching terminal velocity, net force < weight as there is drag acting on the object. drag increases proportional to speed², a < 9.81
-at terminal velocity, net force = 0 as weight = drag, so a = 0


define the moment of a force

force x perpendicular distance to the pivot


state the law of moments

for an object in equilibrium, the SUM of clockwise moments = the SUM of anticlockwise moments


state the principle of moments

for an object in equilibrium, the SUM of clockwise moments = the SUM of anticlockwise moments


what is a couple

a pair of forces that are equal in magnitude but opposite in direction


define the torque of a couple

one of the forces x the perpendicular distance between the forces


what is a centre of mass

a single assumed point, where all of the object's weight acts. can be on or outside of the obejct.


what are the conditions for an object to be in equilibrium

-net force = 0
-sum of clockwise moments = sum of anticlockwise moments


what is density

mass/volume (kg/m^3)


what is pressure

force/area (N/m² or Pa)


what is the upthrust on an object in a fluid

p = (object's height) x (density of the fluid) x g


what is archimedes' principle

an object submerged in water displaces a volume of water equal to its volume; the buoyant force acting on it is equal to the weight of water displaced


define work done by a force

force x distance moved in the direction of the force
W= Fcosθ * x
if the force is not constant, the AVERAGE FORCE must be used


when moving an object, what are the energy conversions

kinetic -> thermal


when an object falls, what are the energy conversions

gravitational potential -> kinetic
an objects gravitational potential energy at the start all converts into kinetic energy at the end, if 100% energy efficiency. energy is wasted as thermal