Motion 1

Question 1

what is an objects weight

Answer 1

mass x gravitational field strength

Question 2

what is tension

Answer 2

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

Question 3

what is upthrust

Answer 3

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

Question 4

what is frction

Answer 4

a force opposing motion

Question 5

what is a normal contact force

Answer 5

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

Question 6

what is drag

Answer 6

the frictional force experienced when travelling through a fluid

Question 7

what factors affect drag when travelling in air

Answer 7

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

Question 8

what is

• thinking distance
• breaking distance
• stopping distance

Answer 8

• 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

Question 9

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

Answer 9

• 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

Question 10

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

Answer 10

• 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

Question 11

define the moment of a force

Answer 11

force x perpendicular distance to the pivot

Question 12

state the law of moments

Answer 12

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

Question 13

state the principle of moments

Answer 13

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

Question 14

what is a couple

Answer 14

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

Question 15

define the torque of a couple

Answer 15

one of the forces x the perpendicular distance between the forces

Question 16

what is a centre of mass

Answer 16

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

Question 17

what are the conditions for an object to be in equilibrium

Answer 17

• net force = 0

- sum of clockwise moments = sum of anticlockwise moments

Question 18

what is density

Answer 18

mass/volume (kg/m^3)

Question 19

what is pressure

Answer 19

force/area (N/m² or Pa)

Question 20

what is the upthrust on an object in a fluid

Answer 20

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

Question 21

what is archimedes’ principle

Answer 21

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

Question 22

define work done by a force

Answer 22

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

Question 23

when moving an object, what are the energy conversions

Answer 23

kinetic -> thermal

Question 24

when an object falls, what are the energy conversions

Answer 24

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