Flashcards in Motion 1 Deck (24):

1

## what is an objects weight

### mass x gravitational field strength

2

## what is tension

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

3

## what is upthrust

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

4

## what is frction

### a force opposing motion

5

## 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

6

## what is drag

### the frictional force experienced when travelling through a fluid

7

## what factors affect drag when travelling in air

###
-velocity (drag ∝ speed²)

-surface area facing the direction of travel

-density of the air

8

##
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

9

##
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

10

## 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

11

## define the moment of a force

### force x perpendicular distance to the pivot

12

## state the law of moments

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

13

## state the principle of moments

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

14

## what is a couple

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

15

## define the torque of a couple

### one of the forces x the perpendicular distance between the forces

16

## 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.

17

## what are the conditions for an object to be in equilibrium

###
-net force = 0

-sum of clockwise moments = sum of anticlockwise moments

18

## what is density

### mass/volume (kg/m^3)

19

## what is pressure

### force/area (N/m² or Pa)

20

## what is the upthrust on an object in a fluid

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

21

## 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

22

## 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

23

## when moving an object, what are the energy conversions

### kinetic -> thermal

24