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Physics Laws of interaction and motion of bodies. Mechanical vibrations and waves. Sound EM field. The structure of the atom and the atomic nucleus.
Topic 1 “Laws of interaction and motion of bodies” Lesson 1. Material point. Reference system. Relocation Yulia Rinatovna Zalyalieva, teacher of physics and mathematics, Secondary School No. 8. 2.09.2015
Movement is an integral property of matter. Movement
Mechanical movement is a change in the position of a body in space relative to other bodies over time. Mechanical movement
Distance traveled; Speed; Trajectory; Move; Body coordinates. Movement characteristics:
Speed is a quantity characterizing the speed of movement. Speed υ (m/s)
Body coordinate - the position of the body in space at any time. Body coordinate
with verbal tabular graphic and analytical (formulas) Methods of describing movement
Verbal description Having left point A, the train traveled for 2 hours at a speed of 100 km/h, then stood for an hour, and arrived at point B 3 hours later, all this time moving at a constant speed of 50 km/h.
Tabular description Graphic description
Analytical description
Ways to describe movement
A material point is a body whose dimensions can be neglected in the conditions of a given problem. Material point
For example, the Earth is often considered a material point when its motion around the Sun is studied.
Can the bodies described in the following situations be considered material points? 1. Calculate the path of the Earth in its orbit around the Sun. 3. To determine the volume of the ball, it is lowered into a beaker. 4. To measure the mass of a lemon, place it on a scale. 5. Your examples
To determine the position of a body (material point) in space, you need to: set a reference body; select a coordinate system; have a device for keeping time (clock)
What is a reference body? A body of reference is a body relative to which the position of other (moving) bodies is determined.
Coordinate system
Reference system:
Let's repeat What is mechanical movement? What is a material point? In what cases can a body be considered a material point? What kind of movement is called translational? What is a frame of reference?
§ 1-2, questions after paragraph Ex. 1 (2,4), Exercise 2 (1) Know all the definitions (!) Homework:
1 point No. Type of movement Definition Examples 1 Translational 2 Rectilinear 3 Rotational 4 Curvilinear 5 Uniform 6 Uneven
A trajectory is a line along which a body moves. The distance traveled is the length of the trajectory. Displacement is a vector connecting the initial position of the body with its subsequent position s (m) s (m)
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Lesson topic. DETERMINING THE COORDINATE OF A MOVING BODY Lesson 2
Scalar and vector quantities trajectory path movement
A trajectory is a line along which a body moves. The distance traveled is the length of the trajectory. Displacement is a vector connecting the initial position of the body with its subsequent position s (m) s (m)
Determination of distance traveled and movement
Task 1. The car has moved from a point with coordinate X 0 = 200 m to a point with coordinate X = -200 m. Determine the projection of the car’s movement. Given: X 0 =200 m X = -200 m S x -? Solution Calculation S x = -200 m -200 m = -400 m Answer: S x = -400 m
Determine from the graph the distance traveled and the module of movement of the material point. S =AB+BC+C D=8 m+4 m+8 m=20 m |S| =A D=4 m
Collection of problems in physics A.P. Rymkevich No. 9 No. 11 No. 17
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Forces in dynamics 11/19/15
Gravity
Gravity
Ground reaction force
Elastic force is a force that arises during deformation of a body, which tends to restore the previous size and shape of the body
HOOKE'S LAW F = - kx k – stiffness coefficient (N/m), depends on the spring material and geometric dimensions x – body elongation (m) x = ℓ 2 - ℓ 1
COMPARISON OF FORCES Gravity force Elastic force Body weight Nature of forces Direction Point of application Depends on Formula
Friction force is the force of resistance to the relative movement of the contacting surfaces of bodies. The friction coefficient μ is a dimensionless quantity. μ
Homework Table Preparation for laboratory work Notebook for laboratory work
Preparation for laboratory work
Determination of friction coefficient
***Exercise. The load rolls down an inclined plane. Draw all the forces acting on the body.
COMPARISON OF FORCES Gravity force Elastic force Body weight Nature of forces Gravitational Electromagnetic Electromagnetic Direction Towards the center of the Earth Against deformation Various Point of application Center of mass of the body Center of mass of the body Support or suspension Depends on the mass of the body and the height above the surface of the spring stiffness coefficient and deformation of the body mass , acceleration, external environment Formula F = mg F = - kx P = m(g±a)
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01/13/16 Oscillatory movement.
What are mechanical vibrations called? What types of vibrations do you know?
FREE vibrations are vibrations that occur under the influence of internal forces after the system has been brought out of equilibrium. FORCED vibrations are vibrations that occur under the influence of external forces. Mechanical vibrations are movements that are repeated exactly or approximately at regular intervals.
List the quantities characterizing oscillations
And Amplitude is the modulus of the largest value of a changing quantity. A [A] = m Oscillation amplitude
A period is the time it takes to complete one oscillation. [T] = с t T = n X , m t ,с 5 2 4 6 8 10 12 Т Т
Frequency is the number of oscillations performed in 1 second. v = n t [ v ] = Hz The unit of measurement is named after the German physicist Heinrich Hertz 1Hz is one oscillation per second. The human heart beats approximately at this frequency v = 1 T
D/z §24-26 (Know the definitions)
Page 105 No. 1-4 Preparation for the test
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Uniform movement in a circle. § 18-19, ex. 18(1)
Mechanical motion Rectilinear (Trajectory - straight) Curvilinear (Trajectory - curve) A O B O A B MOTION
N S Table (top view) Magnet Inclined chute Ball rolled down the chute
Any curve can always be represented as a collection of circular arcs of different radii. DURING CURVILINEAR MOTION, THE following CHANGE: 1) Coordinates 2) Direction of movement 3) Direction and modulus of velocity and acceleration Curvilinear movement is always movement with acceleration, even if the modulus of the speed does not change.
The instantaneous speed of the body at any point of the trajectory is directed tangentially to the trajectory at this point. O A B
Uniform motion in a circle is motion in a circle with a constant absolute speed. A O R R - radius of the circle - initial speed B - final speed When moving uniformly around a circle, its acceleration at all points of the circle is directed towards the center - centripetal acceleration. - centripetal acceleration At any point of the trajectory:
Let's find the acceleration module A B M N Consider ∆AOB and ∆A MN ∆ AOB – isosceles, because OA=BO= R ∆ AMN – isosceles, because Slide 9
According to II Z.N. The force under the influence of which a body moves in a circle with a constant velocity at each point is directed radially towards the center of the circle - a centripetal force. Centripetal force
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MUNICIPAL EDUCATIONAL INSTITUTION DOMODEDOVO SECONDARY SCHOOL No. 2 PHYSICS – 9th grade Physics teacher: SHEKUNOVA Natalya Vladimirovna
Lesson topic: Impulse. Law of conservation of momentum.
The momentum of a body is a vector quantity equal to the product of the mass of the body and its speed:
Momentum p is a vector quantity. It always coincides in direction with the body's velocity vector. Any body that moves has momentum.
Impulse concept
A system of bodies is called closed if the bodies interacting with each other do not interact with other bodies.
In a closed system, the vector sum of the impulses of all bodies included in the system remains constant for any interactions of the bodies of this system with each other. Law of conservation of momentum.
Manifestation of impulse
When firefighters use a cannon, they always have two or even three people holding it. This must be done in order to counteract the impulse of the beating jet.
The law of conservation of momentum using the example of the collision of balls.
Law of conservation of momentum
Give the answer: What is the impulse of a body? Write down the formula for the body's momentum. What is the SI unit of momentum of a body? What is a closed system of bodies? Give examples of the manifestation of the law of conservation of momentum. #17. Task: 1
Problem: On a stationary cart weighing 100 kg. A person weighing 50 kg is jumping. At a speed of 6 m/s. At what speed will the cart with the person begin to move?
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11/13/2015 Newton's laws
QUESTIONS Which reference is called inertial? Non-inertial? Examples. In what case does a body move uniformly? What is a material point called? State Newton's first law? Why does a person who trips fall forward, and a person who slips falls backward? Why doesn't the ball stay at rest on an inclined plane?
QUESTIONS 1. What is called force? 2. How is strength characterized? 3. How do the forces acting on the body add up? 4. What is the direction of the body’s acceleration? 5. Formulate Newton’s second law? 6. What role does mass play in motion? 7. How does the body move if F = 0? 8. How does a body move if a force acts on it?
QUESTIONS 1. State Newton’s third law? 2. What are the features of this law? 3. Give an example of the implementation of Law III. 4. A body is thrown at an angle to the horizontal. Where is the acceleration of the body directed if air resistance is not taken into account?
Newton First law Second law Third law Limits of applicability Macroscopic body System of two bodies Model Material point System of two material points Described phenomenon State of rest or RPD of thruster Interaction of bodies The essence of the law If F = 0, then V = const F 12 = - F 21
How to determine the coordinates of a moving body? To do this, you need to know such concepts as mechanical movement, distance traveled, speed, displacement.
Mechanical movement
During mechanical movement, a change in the position of a body in space relative to other bodies occurs over a period of time. It can be uniform and uneven.
Uniform movement
With uniform motion, a body travels equal distances in equal periods of time (that is, it moves at a constant speed).
The path traveled during uniform motion is equal to: Sx=Vxt=x-xо
Consequently, with uniform motion, the coordinate of the body changes according to the following relationship:
Rice. 1. Formula for the coordinates of a body in rectilinear uniform motion
- Xo– initial coordinate of the body;
- X– coordinate at time t;
- Vx– projection of velocity onto the X axis.
Uneven movement
Uneven motion is a movement in which a body travels unequal distances at equal intervals of time (moves at an inconsistent speed), that is, moves with acceleration.
If a body moves unevenly, then the speed of the body at different moments differs not only in magnitude, but also (or) in direction. The average speed of a body during uneven movement is determined by the formula: V (cf)= S (all)/t (all)
Acceleration – a value showing how the speed changes in 1 second.
Rice. 2. Acceleration formula
Therefore, the speed at any time can be found as follows:
V=Vо+at
If the speed increases over time, then a is greater than 0; if the speed decreases over time, then a is less than 0.
How to find a path in uniformly accelerated motion?
Rice. 3. Rectilinear uniformly accelerated motion
The distance traveled is numerically equal to the area under the graph. That is, Sx=(Vox+Vx)t/2
The speed at any time is equal to Vx=Vox+axt, therefore Sx=Voxt+axt2/2
Since the movement of the body is equal to the difference between the final and initial coordinates (Sx=X-Xo), the coordinate at any time is calculated by the formula X=Xo+Sx, or
X=Xo+Voxt+axt2/2
Vertical body movement
If a body moves vertically and not horizontally, then such motion is always uniformly accelerated. When a body falls down, it always falls with the same acceleration - the acceleration of gravity. It is always the same: g=9.8 m/sq.s.
When moving vertically, the speed formula takes the form: Vy=Voy+gt,
Where Vy and Voy– projections of the initial and final velocities onto the OY axis.
Movement of a body in a circle
When moving in a circle, the numerical value of the speed may not change, but since the direction necessarily changes, movement in a circle is always uniformly accelerated motion.
What have we learned?
The topic “Determination of the coordinates of a moving body,” which is studied in grade 9, will help students systematize information that movement can be uniform and uneven. Also, in order to know the distance traveled, you need to select a reference body and use a device to count time.
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Kinematics solves the main problem of mechanics:
Based on known initial conditions and the nature of movement, the position of the body at any moment in time is determined.
ALGORITHM FOR SOLVING KINEMATICS PROBLEMS
1. Select a convenient coordinate system.
2. Show schematically bodies or material points.
3. Show vectors, initial coordinates, projections of vectors.
4. Write down the basic equations (in vector form or in projections).
5. Find the projections of all known quantities and substitute them into the equations.
6. Solve equations
RULES FOR VECTOR ADDITION
When solving problems in mechanics, the ability to work with vector quantities is required.
How, for example, can we determine the resultant force if several forces act on a body at the same time?
How, for example, can one determine the direction of movement of a swimmer crossing a river if he is carried away by the current?
To do this, one of the vector addition rules will be useful:
Kinematics - Cool physics
Did you know?
Floods on Mars
For a long time, canals on Mars were considered artificial structures built by the inhabitants of Mars. Scientists are still puzzling over the mystery of the origin of the canals today.
According to one hypothesis, Martian canals are the result of floods that occurred on the planet millions of years ago.
Judging by the photographs, Martian canals are very different - from small ones, the size of an average terrestrial stream, to huge ones, hundreds of meters deep and up to two kilometers wide.
According to scientists, there were once huge deposits of ice beneath the surface of Mars. Meteorite falls or processes within the planet caused rapid melting. Streams of water splashed onto the surface and formed channels. Then, in the cold, rarefied atmosphere of Mars, the ice evaporated and partially returned to the planet in the form of snow.
