4 : Forces in action Flashcards
1
Q
net force
A
- a resultant force acting on a object will make an object accelerate in the direction of the force
- f = ma
2
Q
weight of an object
A
- force experienced by a mass due to a gravitational field
- W = mg
3
Q
normal contact force
A
- an object exerts a force on a surface
- the surface exerts an equal and opposite force on the object
- acts perpendicular to the surface
4
Q
equilibrium
A
-forces on body are balanced
5
Q
tension
A
- if string is pulled tight
- force pulling equally on the objects at either end of the string
6
Q
Friction
A
- acting opposite direction of motion
7
Q
mass
A
- an amount of matter
- the greater mass the greater the resistance to a change in velocity
8
Q
centre of mass
A
- the single point the whole weight of object acts through
- object will balance around this point
9
Q
centre of mass and balance
A
- stable if it has low centre of mass and wide base area and lest sable vice versa
- an object will topple over f a vertical line drawn downwards from centre of mass fals outside its base area
10
Q
drag
A
- the resistive force on an object travelling through a fluid (air or water)
- the same as friction
11
Q
upthrust
A
- an upwards buoyancy force acting on an object when it is in a fluid
12
Q
frictional forces
A
- act in opposite directiont o the motion of the object
- convert kinetic energy into heat
13
Q
contact friction
A
- between solid surfaces
14
Q
fluid friction
A
- drag
- depends on viscosity of fluid
increases as speed increases (directly proportional) - depends on shape and size of pbject as well (larger area greater resistive force)
15
Q
terminal velocity
A
- driving force that stays the same all the time
- frictional force tht increases with speed
- resistive force is equal to driving force
- no resultant force and no acceleration
- so constant velocity
16
Q
Skydiver question
A
- skydiver leaves a plane and will accelerate until the air resistance equals weight
- traveling at terminal velocity
- they will open parachute which increases the air resistance (as surface area increases) so it is now bigger than weight
- this slows him down until speed drops enough for air resistance is equal to his weight
- new terminal velocity is smaller
17
Q
affects terminal velocity
A
- liquid - tv will be lower in more viscous liquids as drag is greater
- size - large surface area tv will be lower
- shape - drag force is smaller on moe streamlined shapes
- mass - heavier objects reach a faster tv as greater drag force is needed to balance extra weight
18
Q
density
A
- d = m/v
- Kg m^ -3
- mass per unit volume
density of water is 1g cm^ -3
19
Q
floating
A
- density of an object determines whether it floats
- float if the fluid has a lower density than the object
20
Q
Pressure
A
- amount of force applied per unit area
- Pa (N m^ -2)
- the extra pressure acting n the object due to a fluid depends on the depth of the object the density and the acceleration due to free fall
21
Q
bodies experiencing upthrust
A
- upwards force that fluid exert on objects that are completely or partially submerge in a fluid
- top and bottom of object are at different depths
- create a pressure difference which causes upthrust
- Axpg
- x = distance between top and bottom surface
22
Q
Archimedes principle
A
- upthrust is equal to the weight of the fluid it has displaced
- (h2 - h1)pgA
23
Q
Moment of a force
A
- Nm
- force x perpendicular distance from the pivot to the line of action of the force
- f * x
24
Q
principle of moments
A
- in equilibrium
- sum of the clockwise moments equals the sum of anticlockwise moments
25
Q
lever
A
an effort force acts against a load force rotating around a pivot
26
Q
a couple
A
- a pair of forces of equal size which act parallel to each other but in opposite directions
- produces a turning force
27
Q
torque of a couple
A
- Nm
- size of one of the forces x perpendicular distance between the forces
