Download the presentation on the law of conservation of momentum. Presentation on the topic "body impulse"

Slide 12

Calculations:

A B C As a result of the experiment, we received: m gun = 0.154 kg m projectile = 0.04 kg AC = L gun = 0.1 m L projectile = 1.2 m Using a meter, we determined the time of movement of the projectile and gun, it was: t gun = 0.6 s tprojectile = 1.4 s Now we determine the speed of the projectile and the pistol during the shot using the formula: V = L/t We found that Vpistol = 0.1:0.6 = 0.16 m/s Vprojectile = 1, 2: 1.4 = 0.86 m/s And finally, we can calculate the momentum of these two bodies using the formula: P = mV We received: Pgun = 0.154 * 0.16 = 0.025 kg * m/s Pprojectile = 0.04 * 0 .86 = 0.034 kg*m/s mп*Vп = mс*Vс 0.025 = 0.034 the disagreement was due to the effect of the friction force on the projectile and the error of the instruments. 0.1 m 1.2 m projectile pistol

Slide 13

Virtual test of the law of conservation of momentum

Slide 14

Examples of application of the law of conservation of momentum

The law is strictly observed in the phenomena of recoil when fired, the phenomenon of jet propulsion, explosive phenomena and the phenomena of collision of bodies. The law of conservation of momentum is used: when calculating the velocities of bodies during explosions and collisions; when calculating jet vehicles; in the military industry when designing weapons; in technology - when driving piles, forging metals, etc.

Slide 15

The law of conservation of momentum underlies jet propulsion.

Much credit for the development of the theory of jet propulsion belongs to Konstantin Eduardovich Tsiolkovsky. The founder of the theory of space flight is the outstanding Russian scientist Tsiolkovsky (1857 - 1935). He gave the general principles of the theory of jet propulsion, developed the basic principles and designs of jet aircraft, and proved the need for using a multi-stage rocket for interplanetary flights. Tsiolkovsky's ideas were successfully implemented in the USSR during the construction of artificial Earth satellites and spacecraft.

Slide 16

Jet propulsion

The movement of a body resulting from the separation of part of its mass from it at a certain speed is called reactive. All types of motion, except reactive motion, are impossible without the presence of forces external to a given system, that is, without the interaction of the bodies of a given system with the environment, and for reactive motion to occur, interaction of the body with the environment is not required. Initially the system is at rest, i.e. its total momentum is zero. When part of its mass begins to be ejected from the system at a certain speed, then (since the total momentum of a closed system, according to the law of conservation of momentum, must remain unchanged) the system receives a speed directed in the opposite direction.

Slide 17

Conclusions:

During interaction, the change in the momentum of a body is equal to the impulse of the force acting on this body. When bodies interact with each other, the change in the sum of their impulses is zero. And if the change in a certain quantity is zero, then this means that this quantity is conserved. The practical and experimental verification of the law was successful and once again it was established that the vector sum of the momenta of the bodies that make up the closed system does not change.

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During the classes

1. Organizational stage (1 min)

Report from the duty officer. A desire to work actively and demonstrate your best abilities.

2. Studying new material.(23min)

Guys, the topic of our lesson “Body impulse. Law of conservation of momentum"

Introduction .

Let me begin the study of new material with the statement of Leonardo da Vinci (1452 -1519) we know him as an artist, but he was not only a great painter, but also a great mathematician, mechanic and engineer, to whom the most diverse branches of physics owe important discoveries.

Statement“Knowledge is the daughter of experience”; “The interpreter of nature is experience. He never deceives..."; “Theory is the commander, practice is the soldiers.” But the experiment in itself, without the use of mathematical apparatus, remains an observation.

“No human research can claim to be a true science unless it employs mathematical proof, and there is no certainty where one of the mathematical sciences cannot be applied.”

Today in the lesson we will not only perform experiments, but also prove them mathematically.

Introduction of the concept of momentum

Knowing the basic laws of mechanics, primarily Newton's three laws, it would seem that one can solve any problem about the motion of bodies. Guys, I’ll show you some experiments, and you think, is it possible in these cases to solve problems using only Newton’s laws?

Problem experiment.

Experience No. 1. Rolling a light-moving cart down an inclined plane. She moves a body that is in her path.

The interaction of the cart (short-term collision of the cart and the body, impact) is very small and therefore the strength of their interaction is difficult to determine.

Experience No. 2. Rolling a loaded trolley

Experiment No. 3 Changing the angle of inclination of the plane to increase the speed of a loaded cart

The body moves a greater distance.

Conclusion :

Newton's laws make it possible to solve problems related to finding the acceleration of a moving body if all the forces acting on the body are known, but it is often very difficult to determine the forces acting on the body . As it was in our experiments.

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"Lesson - presentation on physics: "Momentum. Law of conservation of momentum""

Pulse.

Physics teacher MKOU Zonal secondary school

Bezuglov Viktor Viktorovich

• Understand the concept of body impulse
• Study the law of conservation of momentum
• Identify objects and processes from the point of view of the whole and parts
• Compose a learning task based on the correlation of what is already known and learned, and what is still unknown
• Develop the ability to take the initiative in organizing joint action
• Learn to solve problems using the law of conservation

• 1. When the magnet moves quickly over the ball, the ball barely moves from its place; when the magnet moves slowly over the ball, the ball begins to move after the magnet.

• 3. A bullet of mass 10 g moving at a speed of 5 m/s can be stopped by a sheet of cardboard. A bullet with a mass of 10 g moving at a speed of 900 m/s cannot be stopped even with the help of three thick boards.
• 4. Recoil when fired from a gun or gun.

• 1. The result of the interaction of bodies depends not only on the value of the force, but also on the time of its action.
• 2. To characterize the movement of a body, the values ​​of mass and speed of movement are important.
• 3. In a closed system of bodies, the momentum of the system is conserved.

• I - force impulse.
• The impulse of a force is equal to the product of the force vector and the time of its action.
• The direction of the force impulse coincides with the direction of the force.
• [ I ]=[ F ]  [ t ]= newton  second = N  s

• p - body impulse (Rene Descartes, 1596-1650)
• The momentum of a body is equal to the product of the mass of the body and the speed of its movement.
• The direction of the body's momentum coincides with the direction of the body's velocity.
• [ p ]=[ m ]  [  ]=
• kilogram  meter per second = (kg  m)/s

• Newton's laws make it possible to solve problems related to finding the acceleration of a moving body if all the forces acting on the body are known. But it is often very difficult to determine the forces acting on the body.
• Therefore, to solve many problems, another important physical quantity is used - body impulse

• The impulse of a force is equal to the change in the momentum of the body (Newton's second law in impulse form).

• In accordance with Newton's third law of force F 1 And F 2 equal in magnitude and directed in opposite directions:
• F 1 = -F 2
• According to law 2 : m 1 a 1 =- m 2 a 2
• Acceleration : a 1 = (v / 1 – v 1 ) /t ; a 2 = (v / 2 -v 2 ) /t
• m 1 (v / 1 – v 1 ) / t = - m 2 (v / 2 – v 2 ) /t reduce the equation to t
• We get: m 1 (v / 1 -v 1 ) = -m 2 (v / 2 -v 2 )
• Or: m 1 v / 1 – m 1 v 1 =- m 2 v / 2 + m 2 v 2
• Let's group the terms of the equation:
• m 1 v / 1 + m 2 v / 2 = m 1 v 1 + m 2 v 2
• Considering that m v = p
• R / 1 +p / 2 = p 1 + p 2
• The right-hand sides of the equations represent the total momentum of the balls after their interaction, and the left-hand sides represent the total momentum of the balls before interaction
• Projections on the X Axis: m 1 v 1 X + m 2 v 2x = m 1 v / 1x + m 2 v / 2 X

• The vector sum of the momenta of the bodies that make up a closed system remains constant for any interaction of the bodies with each other.

• Reactive movement is the movement of the entire body due to the separation of a part of the body from it.
• For a rocket the formula is:
• where M and m are the masses of the rocket and gas, respectively, u and  are the velocities of the rocket and gas, respectively
• K.E. Tsiolkovsky

• Rockets, jet engines in aviation, astronautics
• Jet boats.
• Movement of living creatures: squid, cuttlefish, octopus

• At what speed will the rocket move if the average speed of the exhaust gases is 1 km/s, and the mass of fuel is 80% of the total mass of the rocket?

• A boy weighing 50 kg jumps from a boat weighing 200 kg moving at a speed of 1 m/s in a horizontal direction at a speed of 7 m/s (relative to the shore). What is the speed of the boat after the boy jumps, if the boy jumps from the stern in the opposite direction to the movement of the boat.

A platform with sand weighing 20 tons moves along the railway track at a speed of 1 m/s. It is caught up with a projectile weighing 50 kg flying horizontally at a speed of 800 m/s and crashes into the sand without an explosion. At what speed will the platform with the projectile stuck in the sand move?

• An athlete (his mass is 80 kg) stands on skates on smooth ice and holds a cannonball weighing 8 kg in his hands. He then throws the cannonball horizontally; the latter acquires a speed of 20 m/s relative to the ice. How fast will the athlete move after the push?

Solving impact problems

• CONDITION:

What is it equal to v 1 gun recoil m 1 = 4 kg when firing a bullet m 2 = 5 g s v 2 = 300 m/s?

• Projectile m 1 = 100 kg flying from v 1 =500m/s, falls into a car with sand m 2 = 10 t and gets stuck in it. What speed v' 2 acquires a carriage if it was moving towards the projectile with v 2 = 10m/s?

• CONDITION:
• The projectile, flying at a speed of 500 m/s, exploded into two fragments. The speed of the first fragment weighing 5 kg increased by 200 m/s in the direction of the projectile movement. Determine the speed of the second fragment if its mass is 4 kg.

• § 21.22
• ex. 20(2), 21(1)
• textbook A.V. Peryshkin, E.M. Gutnik “Physics-9”.
• If you wish, you can draw pictures on the topic you have studied.

• V. Ya. Lykov Aesthetic education in teaching physics. Book for teachers. -Moscow “ENLIGHTENMENT” 1986.
• V. A. Volkov Lesson developments in physics grade 9. - Moscow “VAKO” 2004.
• A. A. Kharitonova History of physics textbook - Saransk 2003.
• Edited by Professor B.I. Spassky. Reader on physics. -MOSCOW “ENLIGHTENMENT” 1987.
• I. I. Mokrova Lesson plans based on the textbook by A.V. Peryshkin “Physics. 9th grade.” - Volgograd 2003.

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Slide captions:

Pulse. Law of conservation of momentum. Presentation made by Physics Teacher, Secondary School No. 507 Pavlyuk A.I. St. Petersburg 2011

About immutability in the world... “I accept that in the Universe... there is a certain amount of motion that never increases or decreases, thus, if one body sets another in motion, it loses as much of its motion as it imparts.” In the 17th century, quantities that persist in certain phenomena were first indicated.

Pulse. Law of conservation of momentum. Body impulse. Impulse of force. Law of conservation of momentum. Application of the law of conservation of momentum - reactive motion.

Explain the phenomena...

Newton's second law F=ma a = v- v 0 / t Ft = mv - mv 0 p = m v - body impulse p = kg m/s SI Ft - force impulse. mv - mv 0 – change in body pulse

Newton's second law in impulse form: The impulse of a force is equal to the change in the momentum of the body. Momentum is a vector quantity. It always coincides in direction with the velocity vector.

If two or more bodies interact only with each other (are not exposed to external forces), then these bodies form a closed system. The momentum of each of the bodies included in a closed system can change as a result of their interaction with each other. There is a very important law for the description - the law of conservation of momentum.

Law of conservation of momentum: The vector sum of the impulses of a closed system of bodies does not change.

Absolutely elastic impact - a model of impact in which the total kinetic energy of the system is conserved 1. identical bodies exchange velocity projections on a line connecting their centers. 2. The speeds of bodies of different masses depend on the ratio of the masses of the bodies.

For a mathematical description of the simplest absolutely elastic impacts, the following is used: the law of conservation of momentum, the law of conservation of energy, an absolutely elastic impact of bodies of unequal masses. Momentums add up vectorially, and energies add up scalarly! absolutely elastic collision of bodies of equal masses

Central absolutely elastic impact When both balls have the same masses (m 1 = m 2), the first ball stops after the collision (v 1 = 0), and the second moves with a speed v 2 = v 1, i.e. the balls exchange velocities (moments ) A central impact of balls is a collision in which the velocities of the balls before and after the impact are directed along the line of centers.

After a non-central elastic collision, the balls fly apart at a certain angle to each other. If the masses of the balls are the same, then the velocity vectors of the balls after a non-central elastic collision are always directed perpendicular to each other

An absolutely inelastic impact is an impact, as a result of which the velocity components of the bodies become equal. With an absolutely inelastic impact, the law of conservation of momentum is satisfied, but the law of conservation of mechanical energy is not satisfied (part of the kinetic energy of colliding bodies, as a result of inelastic deformations, turns into thermal energy)

Jet motion Jet motion is a movement that occurs when some part of it is separated from the body at a certain speed. The peculiarity of this movement is that the body can accelerate and decelerate without any external interaction with other bodies.

Jet propulsion, for example, is performed by a rocket. During departure, combustion products receive a certain speed relative to the rocket. According to the law of conservation of momentum, the rocket itself receives the same momentum as the gas, but directed in the other direction. The law of conservation of momentum is needed to calculate the speed of a rocket.

TASK: Before launching the rocket M r υ r =0, m g υ g =0 After launch At what speed will the rocket move if the average speed of the exhaust gases is 1 km/s, and the mass of the fuel is 80% of the total mass of the rocket? m r υ r m g υ g

Jet motion in wildlife: Jet motion is inherent in jellyfish, squid, octopuses and other living organisms.

Jet motion can also be found in the plant world. In southern countries and on our Black Sea coast, a plant called “mad cucumber” grows. When the seeds ripen, high pressure is created inside the fruit, as a result of which the fruit is separated from the substrate, and the seeds are thrown out with great force. The cucumbers themselves fly off in the opposite direction. The “mad cucumber” shoots at more than 12 meters.

In technology, jet propulsion is found in river transport (a boat with a water-jet engine), in aviation, astronautics, and military affairs.

A light ball moving at a speed of 10 m/s collides with a heavy ball at rest and an absolutely elastic impact occurs between the balls. After impact, the balls fly off in opposite directions at equal speeds. How many times do the masses of the balls differ? Solution:

A block of mass 600 g, moving at a speed of 2 m/s, collides with a stationary block of mass 200 g. Determine the change in kinetic energy of the first block after the collision. The impact is considered central and absolutely elastic. Solution:

Two balls with masses of 200 g and 600 g, respectively, hang in contact on identical vertical threads 80 cm long. The first ball is deflected at an angle of 90° and released. What will be the ratio of the kinetic energies of the heavy and light balls immediately after their absolutely elastic central impact? Solution:

A ball with a mass of 100 g, flying horizontally at a speed of 5 m/s, absolutely elastically hits a stationary ball with a mass of 400 g, hanging on a thread 40 cm long. The impact is central. At what angle will a ball suspended on a string deflect after an impact? Solution.

Slide 1

Presentation made by Physics Teacher, Secondary School No. 507 Pavlyuk A.I. St. Petersburg 2011

Slide 2

About immutability in the world...
“I accept that in the Universe ... there is a certain amount of motion that never increases or decreases, thus, if one body sets another in motion, it loses as much of its motion as it imparts.”
In the 17th century, quantities that persist in certain phenomena were first indicated.

Slide 3

Pulse. Law of conservation of momentum.
Body impulse. Impulse of force. Law of conservation of momentum. Application of the law of conservation of momentum - reactive motion.

Slide 4

Explain the phenomena...

Slide 5

Newton's second law F=ma a = v- v 0 / t Ft = mv - mv0 p = mv - body impulse p = kg m/s SI Ft - force impulse. mv - mv0 – change in body pulse

Slide 6

Newton's second law in impulse form: The impulse of a force is equal to the change in the momentum of the body. Momentum is a vector quantity. It always coincides in direction with the velocity vector.

Slide 7

If two or more bodies interact only with each other (are not exposed to external forces), then these bodies form a closed system. The momentum of each of the bodies included in a closed system can change as a result of their interaction with each other. There is a very important law for the description - the law of conservation of momentum.

Slide 8

Law of conservation of momentum:
The vector sum of the impulses of a closed system of bodies does not change.

Slide 9

Slide 10

Absolutely elastic impact - a model of impact in which the total kinetic energy of the system is conserved
1. identical bodies exchange velocity projections onto a line connecting their centers. 2. The speeds of bodies of different masses depend on the ratio of the masses of the bodies.

Slide 11

For a mathematical description of the simplest absolutely elastic impacts, the following is used: the law of conservation of momentum, the law of conservation of energy, an absolutely elastic impact of bodies of unequal masses. Momentums add up vectorially, and energies add up scalarly!
absolutely elastic collision of bodies of equal masses

Slide 12

Central absolutely elastic impact
When both balls have the same masses (m1 = m2), the first ball stops after the collision (v1 = 0), and the second moves with a speed v2 = v1, i.e. the balls exchange velocities (moments). The central impact of the balls is a collision in which the velocities of the balls before and after the impact are directed along the line of centers.

Slide 13

After an off-central elastic collision, the balls fly apart at a certain angle to each other
If the masses of the balls are the same, then the velocity vectors of the balls after an off-central elastic collision are always directed perpendicular to each other

Slide 14

Slide 15

Absolutely inelastic impact - an impact as a result of which the velocity components of the bodies become equal
With an absolutely inelastic impact, the law of conservation of momentum is satisfied, but the law of conservation of mechanical energy is not satisfied (part of the kinetic energy of the colliding bodies, as a result of inelastic deformations, turns into thermal energy)

Slide 16

Jet propulsion
Reactive motion is a movement that occurs when some part of it is separated from the body at a certain speed. The peculiarity of this movement is that the body can accelerate and decelerate without any external interaction with other bodies.

Slide 17

Jet propulsion, for example, is performed by a rocket.
During departure, combustion products receive a certain speed relative to the rocket. According to the law of conservation of momentum, the rocket itself receives the same momentum as the gas, but directed in the other direction. The law of conservation of momentum is needed to calculate the speed of a rocket.

Slide 18

TASK: Before the rocket launch Mрυр=0, mгυг=0 After launch
At what speed will the rocket move if the average speed of the exhaust gases is 1 km/s, and the mass of fuel is 80% of the total mass of the rocket?
mrυr
mgυg

Slide 19

Jet propulsion in wildlife:
Jet motion is inherent in jellyfish, squid, octopuses and other living organisms.

Slide 20

Jet motion can also be found in the plant world. In southern countries and on our Black Sea coast, a plant called “mad cucumber” grows. When the seeds ripen, high pressure is created inside the fruit, as a result of which the fruit is separated from the substrate, and the seeds are thrown out with great force. The cucumbers themselves fly off in the opposite direction. The “mad cucumber” shoots at more than 12 meters.