REVISION NEWTON’S LAW. Quantity with magnitude and direction. e.g. displacement, velocity,...
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Transcript of REVISION NEWTON’S LAW. Quantity with magnitude and direction. e.g. displacement, velocity,...
REVISIONNEWTON’S LAW
Quantity with magnitude and direction.
e.g. displacement, velocity, acceleration, force and weight..
VECTORQuantity having only
magnitude, not direction. e.g. distance, speed, mass
SCALAR
Earth's gravitational pull on an object.
It is measured in Newton
WEIGHTThe measure of the amount of matter
contained in the object.It is measured in kilograms
MASS
RESULTANTE/NET VECTOR The single vector that will have the same effect as all the other
vectors will have together
FORCES
WEI
GHT
NO
RMAL FO
RCE
APPLIED FORCE
DIRECTION OF MOTION
FRICTIONAL FORCE
FORCE DIAGRAM
FREE BODYDIAGRAM
normaal forceF Gravitational force (weight)
kinetic frictional forceF force of cat on box
N
g
k
T
KEYF
f
DIRECTIONS
• 300o • 30o North of West • West 30o North
NEWTON'S FIRST LAW OF MOTIONA body will remain in its state of rest or motion at
constant velocity unless a non-zero resultant/net force acts on it.
NEWTON'S SECOND LAW OF MOTION
When a resultant/net force acts on an object, the object will accelerate in the direction of the force at an acceleration directly
proportional to the force and inversely proportional to the mass of the object.
Fres=ma
NEWTON'S THIRD LAW OF MOTIONWhen one body exerts a force on a second body, the second body exerts a force of equal magnitude in the
opposite direction on the first body
NEWTON'S THIRD LAWACTION-REACTION PAIRS1. Same magnitude, opposite direction2. Simultaneous3. Only two objects
the force or the component of a force which a surface exerts on an object with which it is in contact, and which is perpendicular to
the surface
NORMAL FORCE
WEIGHTgravitational force the Earth exerts on any object on or near its
surface
the force that opposes the motion of an object acts parallel to the surface.
– Perpendicular on normal force– independent of the area of
contact – independent of the velocity of
motion
FRICTIONAL FORCE
STATIC FRICTIONAL FORCE the force that opposes the tendency
of motion of a stationary object relative to a surface
KINETIC FRICTIONAL FORCE the force that opposes the motion of a
moving object relative to a surface
Nf F
• Is usually given• It depends on the 2 surface areas that are in
DIRECT contact• This is the relationship between the friction force
and the normal force of an object (the coefficient of friction therefor has no unit of measure)
COEFFICIENT OF FRICTION
N
fF
Forces acting on an object. Pushing or pulling forces
APPLIED FORCE
TENSION Force in a stretched rope
RESULTANT / NET VECTORThe single force that will have the same effect as all the other
forces will have together
FORCE DIAGRAMS
FORCE DIAGRAMS
FORCE DIAGRAMS
normal forceF Gravitation (weight)
frictionF Applied force
N
g
T
F
f
sin cos
cossin
cossin
y x
TT
x Ty T
o ah hF F
FFF FF F
normal forceF Gravitation (weight)
frictionF Vertical komponent of pplied force
F Horizontal komonent of pplied force
N
g
y
x
F
fa
a
FORCE DIAGRAMS
FORCE DIAGRAMS
||
normal forcefriction
F Vertical komponent of weight
F Vertical komponent of weight
N
g
g
Ff
||
||
sin cos
sin cos
sin cos
g g
g g
g g g g
o ah hF F
F F
F F F F
EQUILIBRIUMNEWTON’S PROBLEMS
PERPENDICULAR FORCES (equilibrium)
‘ANGLED’ FORCES (equilibrium)
A box with mass 5kg stands stationary on a horizontal plane, experiencing a 10N applied force at an angle of 30o
ANGLED PLANES (equilibrium)
TRIANGLES for EQUILIBRIUM with THREE FORCES
non-EQUILIBRIUMNEWTON’S PROBLEMS
PERPENDICULAR FORCES (non-equilibrium)
‘ANGLED’ FORCES (non-equilibrium)
o
A block of mass 1 kg is connected to another block of mass 4 kg by a light inextensible string.
The system is pulled up a rough plane inclined at 30 to the horizontal, by means of a constant 40 N force parallel to the plane as shown in the diagram above.The magnitude of the kinetic frictional force between the surface and the 4 kg block is 10 N. The coefficient of kinetic friction between the 1 k
g block and the surface is 0,29. State Newton's third law in words.
Draw a labelled free-body diagram showing ALL the forces acting on the 1 kg block as it moves up the incline.
Calculate the magnit
a
b
ude of the: Kinetic frictional force between the 1 kg block and the surface
Tension in the string connecting the two blocks
c
d
||
||
o o
For the 1kg block
sin cos
sin cos
sin cos
1 9.8 sin 30 1 9.8 cos 30
g g
g g
g g g g
o ah hF F
F F
F F F F
||
||
o o
For the 4kg block
sin cos
sin cos
sin cos
4 9.8 sin 30 4 9.8 cos 30
g g
g g
g g g g
o ah hF F
F F
F F F F
o
see left
0.29 8.48take up as positive2.46 down
0
1 9.8 cos 308.48
N
res
N g
N g
ay axis f Fb
F ma NF F
F F
N
||
o
for 1kg block-
take up as positiveF
40 2.45 1 9.8 sin 30 132.6 1
for 4kg block
res
T g
cx axis
maF f T F ma
T aT a
||
o
for 4kg block-
take 'up' as positiveF
10 4 9.8 sin 30 429.6 4
res
g
c
x axis
maT f F ma
T aT a
2
T=T Susbtitute a in 29.6 432.6 1 29.6 4 29.6 4 0.6
3.03 5 32.030.6 . up
let T aa a
a Na m s
||
||
o o
For the 1kg block
sin cos
sin cos
sin cos
1 9.8 sin 30 1 9.8 cos 30
g g
g g
g g g g
o ah hF F
F F
F F F F
||
||
o o
For the 4kg block
sin cos
sin cos
sin cos
4 9.8 sin 30 4 9.8 cos 30
g g
g g
g g g g
o ah hF F
F F
F F F F
o
||
o
see left
0.29 8.48take up as positive2.46 up
0
1 9.8 cos 30
8.48for 1kg block
-take up as positive
F
40 2.45 1 9.8 sin 30 1
32.6 1for 4kg bloc
N
res
N g
N g
res
T g
a
y axis f Fb
F ma NF F
F F
Nc
x axis
maF f T F ma
T a
T a
||
o
2
k-
take 'up' as positiveF
10 4 9.8 sin 30 4
29.6 4
T=T Susbtitute a in 29.6 432.6 1 29.6 4 29.6 4 0.6
3.03 5 32.030.6 . up
res
g
x axis
maT f F ma
T a
T a
let T aa a
a Na m s
ELEVATORS
GRAPHIC SOLUTIONSNEWTON’S PROBLEMS
HEAD-TO-TAIL METHOD– EQUILIBRIUM with THREE FORCES
HEAD-TO-TAIL METHOD– EQUILIBRIUM with maximum
tension/weight
GRAPHIC SOLUTIONS for NON-EQUILIBRIUM
NEWTON’S UNIVERSAL GRAVITATIONAL LAW
NEWTON'S UNIVERSAL GRAVITATION LAW
Each body in the universe attracts every other body with a force that is directly proportional to the
product of their masses and inversely proportional to the square of the distance between their centres
1 22
Gm mF
r
GRAVITATIONAL ACCELERATION FOR ANY PLANET1 22 g
Gm mF F mg
r
2
2
2
g
o po
o p
o
p
F F
Gm mm g
rGm m
gr mGm
gr
There is a gravitational force F between objects A and B at a distance R from each other. What will the gravitational force be if the mass of A is doubled and the distance of separation
made three ti 29mes greater ? F
RATIO PROBLEMS
RATIO PROBLEMS
22 2
2 2
2
3
2329
A B Ai f
A B
i
km m k m mF FR R
km mR
F
363 , 517 aThree spheres li
nd 154 e stationary in a straight line.
The masses of the spheres are Determine the magnitude and direction of the net gravitatio ...
Sphere A
nal force
5.7
onA B Cm kg m kg m kg
a
5
5
5
10 right
3.5 10 right Sphere B
Sph 9 10 er lefe C t
b
c
N
N
N
NET GRAVITATIONAL FORCE
NET GRAVITATIONAL FORCE
2
11
2
11 5
2
11
2
11 6
between A & B?363517 6.67 10 363 5170.5 0.5
6.67 10 5 10 between A & C
?363154 6.67 10 363 1540.75 0.7
take right
56.67 10 6.6 10
AB A BAB
ABA
B
AB
AB A CAC
ACA
C
AC
FF Gm m
Frm
mr
G NF
F Gm mF
rmmr
G N
5 6
5
:
5 10 6.6 10
5.7 10 re
as posit
gs
ive
net AB ACA F F Fa
N
NET GRAVITATIONAL FORCE
2
11
2
11 5
2
11
2
11 5
between A & B?363517 6.67 10 363 5170.5 0.5
6.67 10 5 10 between B & C
?517154 6.67 10 517 1540.25 0.2
take right
56.67 10 8.5 10
AB A BAB
ABA
B
AB
AB B CBC
BCB
C
BC
FF Gm m
Frm
mr
G NF
F Gm mF
rmmr
G N
5 5
5
:
8.5 10
as posit
5 10
3.5 10 re
v
gs
i e
net BC ABB F F Fb
N
NET GRAVITATIONAL FORCE
2
11
2
11 6
2
11
2
11 5
between A & C?363154 6.67 10 363 1540.75 0.75
6.67 10 6.6 10 between B & C
?517154 6.67 10 517 1540.25 0.25
6.67 10 8.5r
10take
AB A CAC
ACA
C
AC
AB B CBC
BCB
C
BC
FF Gm m
Frm
mr
G NF
F Gm mF
rmmr
G N
6 5
5
5
:
6.6 10 8.5 10
9 10
9 10 l
ight as positive
inks
net AC BCC F F Fc
N
N