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Transcript of sejarah fisika
CHAPTER 3
MOTION AND FORCES IN MORE THAN ONE DIMENSION
By :Ari Dewayani (12316244010)Navis Aininah (12316244016)
One thing wa clear about beginning and end points
the path of a projectiles wa difficult for the acients
to trace
Solved :
Fig 3-1
connon
Fig. 3-1. A cannon or a caapult must direct a procectile at an angle above the horizontal line to hit a distant object on the same level.
Gallileo’s
Projectile falls verticaly as moves horizontals
In terms of forces produce curvacture aided the discription of curved motion in general
3-1 Direct Quantities : Vectors
The east-west line The North-South line The vertical or artitude line
Direction for a fairly small region of the earth’s surface
Directed Quantity displacement tof the point of a pencil from one place on a notebook page to another is called vector.
Displacement : relative position depends only on initial and final positions and is independent of the path beteween.Fig 3-2 Two actual displacements are made, but they result in the single vector OP. Vector OP is the sum of vectors OA dan OP.
1.4 in
1 in
1 in A
E
P
O
Displacement from O to P
Fig 3-4
A line segment whose length represents its magnitude in accord with some predetermined scale, and whose direction is that of the force. The two may be added as though they were displacements and the magnitude of the vector sum or resultant.On the first law of motion, since equilibrium is defined as an absence of accelertion.
2 lb
C
B
20 lb
A
D
Two forces acting at the same point but in different direction represented in the figure.
A detailed diagram showing just how forces are distributed in a given equilibrium in nonetheless extremely useful in practice. (Fig 3-5)
The physical problem supporting a 100lb object by two strings in the manner shown in (a) maybe analyzed by a force diagram (b) The resultant sum R of the forces T1and T2 exerted by the strings must be equal and opposite to weight w.
100lb
30° 60°
R
T1
T2
W
Figure 3-6 which is velocity diagram, is applicable only to individual instans of time, no indicationshow long those conditions prevail.
In practice, a single velocity can be specified by giving its magnitude (speed) and appropriate angles for describing its direction, but diagram is invalube for determining the net result of two simultaneous velocities.
3-1 Motion of Projectiles
The correct of Galilleo disregarded fallacious views at once in terms of Gallileo’s discoveries about falling bodies and the most elementary ideas contained in Newton’s Law.Law of inertia a state either of rest or of uniform motion in horizontal direction is then maintaned unaltered.
Gallileo
Work out the parabolic path for a projectile
The horizontal motion was uniform while the
simultaneous downward motion was uniformly accelerated
The important point is that the motion of the horizontally fired ball, neglecting air resistance, is made up teo independent but simultaneous parts, manifested in two perpendicular direction.Actual path o16ft
64ft
144ft
1. Actual velocities different instans2. Other features of the motion
o 40ft 80ft 120ft 160ft
1sec
2sec
3sec
4sec
Position shown are those at the end of the 1st, 2nd, 3rd and 4th second of fall from a tower 256 ft high . Thr path on the left is that of a body which is dropped and the curved (parabolic path of a body fired horizontally at a speed of 40 ft/sec. (Figure 3-7)
Uniform horizontal velocity the ball in its flight, if the cart also moves at steady speed it will catch the ball when the latter returns to the horizontal level from which it was fired. Figure 3-8
Fig. 3-8. Ball projected upward from a cart in uniform motion keeps abreast of the cart as it rises and falls
3-3 Uniform Circular Motion
Huygens’ word “Maintain forever a motion once impressed upon it.”In the absence of forces, however since the earth is curved, the object would progressively from the earth’s surface. (Figure 3-9).
Object fired horizontally from top of tower at various speeds strikes earth at various distance. With unifrom velocity it would recede from the earth surface.
Uniform velocity
For projectiles subject to the inescapable influence of gravity, fired at great horizontal speeds, the effect of the earth curvature would be to make the time of fall a little greather than expected from Galileo’s Law of free fall.
Principle
It should be possible to fire at a bullet with a speed so great that it falls toward the earth at the same rate that the earth’s surface recedes from it bcause of the earth urvature
If there were no air friction and no obstacles, it could continue to go
around earth at a constant distance from its center
Figure 3-10
The distance such a projectile would travel in a time t if there no gravity. Let y represent the distance fallen in this same time, such that the projectile maintains its original distance from the center of the earth.
d is perpendicular to the radius of the earth at the starting point we use theorem of pythagoras, then we get :
d2 = y2 + 2ry
According to Galileo’s of free fall :
y =
Represent the speed by v := α r, so
Summary• The world is three-dimensional, and changes in
motion may include change in direction as well as in speed.
• Directed quantities called vectors• A body in uniform circular motiojn is accelerated
toward the center of the circle although its speed remains constant.
• Cetripetal is required to produce this acceleration
• Galileo was able to achieve the first satisfactory account of projectile motion.
• The rotation of the earth about its axis involves such forces.