Two questions of physics concepts in high school, two questions of physics in high school

1. Acceleration and velocity are the same, it is a vector, there is a size and a direction, when solving the problem, it is necessary to determine a positive direction (generally the direction of initial velocity is positive), such as the right is positive, if the acceleration direction is left, it is a negative value. Acceleration is provided by the resultant external force on the object, and the direction of the resultant external force is the direction of acceleration, such as an object moving at a uniform speed to the right, and you give a thrust to the right, the acceleration of the object is the same as the force, and his velocity will increase at this time; Conversely, if the force given is to the left, physics will slow down at this point.

2. Yes, strictly speaking, the physical displacement should be 0, and the instantaneous velocity may not be 0; The key to understanding is to grasp the concept of displacement (a directed line segment from the initial position to the final position, which is the distance between the initial position and the last position, and the direction is from the initial position to the last position).

Example: A person is running on the playground and he returns to the starting point after a lap, at this point he has a velocity, but the displacement is 0.

1.Acceleration, as the name suggests, is the increment of velocity per unit of time.

If the increment of velocity per unit of time is positive, that is, the acceleration and velocity are in the same direction, then it must be accelerated, and if the increment of velocity per unit time is negative, that is, the acceleration and velocity are in opposite directions, then it must be decelerating.

2.That's right. For example, if a small ball is thrown vertically upwards, when the ball falls back to the throwing point, its displacement is zero, but the velocity is there, and the direction is vertically downward.

What you have to figure out is that all quantities with magnitude and direction are vectors, and velocity, acceleration, and displacement are vectors.

The positive and negative signs of these vectors are only used to determine the direction, and of course they are based on the initial state.

For example, if the direction of the initial velocity is positive, if the acceleration is negative, it means that the direction of the acceleration is opposite to the direction of the initial velocity.

Acceleration is equal to the final velocity minus the initial velocity divided by the motion time, so the positive or negative acceleration reflects the magnitude relationship between the initial and final velocity of the object, so it is not difficult to conclude that the second problem, the situation may arise, for example, a collision, the object can gain velocity instantaneously through the collision, but at the same time its displacement is zero.

The first is the understanding of the concept of acceleration, the direction of acceleration is the same as the direction of the change (or increment) of velocity, and when the direction of velocity change is the same as the direction of velocity, the velocity of course increases, and vice versa, deceleration, that is, acceleration and reverse deceleration in the same direction as velocity, the first half of the statement is correct.

However, if you accelerate, the direction of acceleration and the direction of velocity are not necessarily the same, because acceleration is a vector, as long as the angle between the acceleration and the direction of velocity is less than 90 degrees, the object can be accelerated; When the angle between acceleration and velocity is greater than 90 degrees, the object will slow down, which will be covered in high school physics compulsory 2. The second half is also possible if it is in a linear motion.

The second question is to throw a small ball vertically upwards, when the ball falls back to the throwing point, its displacement is zero, but the velocity is, and the direction is vertically downward.

In the first question, the insulated metal spherical shell A should be positively charged, right? Otherwise, there is no way to judge! Is C grounded after electrostatic equilibrium?

Assuming A turns out to be positively charged, the answer is BC. It's hard to explain, add me and I'll tell you slowly!

The answer to the second question is c. Due to the equipotential of AB, A induces a positive charge, B induces an equal amount of negative charge, and the AB potential is greater than zero (the ground potential is zero), and after touching B with your hand, the AB potential is zero, that is, the positive charge of ball A will be introduced to the earth (outside of the power supply, the current always flows from high potential to low potential), and ball B is still negatively charged, which is induced!

1. Judgment. 1. As long as there is an object, there must be a strong existence Yes, the force cannot exist independently of the object.

2. The shape of the object changes, and the object is not necessarily subjected to force is wrong, it is the effect of force.

3. Block A is placed on a horizontal tabletop, and the block has a pressure perpendicular to the table due to a slight deformation That's right, it's elasticity.

4. The direction of friction must be perpendicular to the direction of pressure.

5. The direction of elastic force must be perpendicular to the direction of friction.

1 correct. 2 Errors.

3 correct. 4 correct.

5 Errors. 6 two elastic forces.

x x v x x, two bars.

Force is generated by the interaction of objects, how can there be force when there is only one object?

1. That's right, because as long as it's an object, it's at least subject to gravitational attraction!

Let's start with e=w q, which is a scalar formula.

q is generally taken as an absolute value (if you bring +, - it is useless to affect the level of electromotive force and the direction of particle motion).

The electromotive force is a scalar quantity, not about the direction, but about the high and low.

Before we get to the point, let's say a little bit:

The electric field in the wire is the vector sum of the electric field formed by the electric field of the power supply and the moving charge in the wire, whereas the electric field of the power supply is a non-conservative field.

====Specific analysis *****===

1. The electric field in the energized wire is the vector sum of the electric field formed by the electric field of the power supply and the moving charge in the wire.

Note is the movement of the charge!

Whereas, the electrostatic equilibrium must be steady state for the charge to be all at rest.

2. The electric field of the power supply is a non-conservative field, and the electrostatic field is a conservative field.

It's very unclear in the textbooks, so I suggest you take a look at the college physics books.

The definition of an electrostatic field is: an electric field that is excited by a stationary charge (as opposed to the stationary charge of the observer) and the above two questions you gave are when the wire is energized. There is no electrostatic field, but an induced electric field excited by an energized wire.

There are positive and negative charges, there are positive charges and negative charges, the electromotive force e has positive and negative poles, the positive electrode has a positive charge, and the negative electrode has a negative charge.

Hope it helps.

1. Definition of electrostatic equilibrium state: the state in which there is no charge in the conductor to make any macroscopic directional motion. The necessary condition for the electrostatic equilibrium of a conductor is that the electric field strength at any point in the conductor is equal to zero. Therefore, energized wires are not electrostatically balanced.

2. It is clear that the charge in the wire is in motion, so it is not an electrostatic field!!

e is a vector and has a direction. The direction of e is from the positive charge to the negative charge.

1. AB as a system, the friction force on A is m0*g, and the friction between AB and AB in the direction of M0*G is 0 (because B moves at a uniform speed and is not affected by external force).

2. According to the analysis of the force on M1, the tensile force of the M1 uniform motion spring to it is U*M1*G, so the elongation of the spring is (U*M1*G) K, so the distance between the two objects is (U*M1*G) K+L

If you still don't understand the friction, feel free to find me!

Question added: b will not be pulled! There will be no friction between ABs!

Because if there is an external force acting on B, then B will definitely accelerate under the action of external force, and it is impossible to move at a uniform speed, and the condition for doing uniform motion is: the object is not affected by force (balanced or not forced in a certain direction) The object moves at a uniform speed!

To do this problem, the problem of superimposing objects is to analyze the top object first, because the top is less stressed, it is easier, and then analyze it downwards in turn!

1.To the left, mog

Since the object moves at a uniform speed as a whole, the tensile force of the rope is equal to the gravitational force mog of c, and because the tensile force of the same rope is the same, the frictional force is equal to the tensile force mog

The friction between AB is 0, because for B object, if there is friction, it is impossible to move together with A at a uniform speed.

2. (m1gμ+kl)／k

Let the distance between the two wooden blocks be x, for m1, if you want to move at a uniform speed, the friction force = the elastic force of the spring, that is, f = m1g = k(x-l).

So the distance between the two wooden blocks (m1g +kl) k

Friction is the force of the ground supporting an object multiplied by a coefficient of friction.

1. Treat AB as a whole, analyze the force, the right tension, the left friction, and the equivalent reversal.

So left; m0g；

Re-analysis b, the constant velocity is in equilibrium, and there is no force in the horizontal direction, so 0;

f=kxs=l+x

s is the distance.

1.It may be 0 because it is averaged over a period of time, and the velocity is a vector with directions, for example, if an object moves in one direction at a uniform speed for 5 seconds, and then moves in the opposite direction at the same rate for 5 seconds, then its average velocity in these 10 seconds is 0

2.The speed at which the raindrops pass through the window is the average velocity, because the raindrops pass through the window which is a process that takes a while, and of course it also goes through a period of displacement, not an instantaneous velocity, which should be the average velocity.

Average speed with direction! It can be a reciprocating exercise! For example, from A to B and from B back to A, then its displacement is 0, the average velocity is 0, and the average velocity is calculated by displacement, not distance! Average rate with distance!

The second is the average speed because the length of the window is a process, not a point!

It's important to ask questions, not questions, because it may be naïve for others to ask questions.

Do you think it's true that the average velocity of a moving object for a certain period of time cannot be zero?

1: Set A v 2a B -a

v+8a=8

v=4 a=1//2

2: v1=v2= The direction is opposite to the original direction.

1.The current has direction, but it is a scalar quantity, not a vector quantity. The essence of vectors is to follow the rules of vector arithmetic (high school math content, which you will talk about in math textbooks when you wait until your sophomore year of high school).

Regarding the direction of the current, we must start with the concept of the current. The concept of electric current is the directional movement of electric charge, and we stipulate that the direction of movement of positive charge is the direction of electric current.

2.Heat is a scalar quantity. The flow from a place with a high temperature to a place with a low temperature is the direction of heat conduction, and the accompanying change in internal energy is called heat.

The heat itself has nothing to do with high and low temperatures, so this direction cannot be counted as the direction of heat. And as mentioned in 1, what has direction is not necessarily a vector (the method of defining vectors in junior high school is for ease of understanding), and there are many directional scalars in the back.

3.The velocity is indeed a vector quantity, and the direction is the same as the direction of displacement. What you call circular motion is actually confusing the concepts of average velocity and instantaneous velocity.

In a circular motion, the direction of the instantaneous velocity is the same as the direction of its instantaneous displacement, but since it is only instantaneous, no actual displacement is generated. At each moment of motion, the direction of velocity is along the tangent direction of the curve. The average velocity of a circle in a circular motion is 0 because it has no displacement, and here the velocity is also in the same direction as the displacement.

Hopefully, you can ask me any more questions.

1.Electric currents have directions, you just need to know them, because by the time you reach high school, you will learn about the movement of electric charges, which are all calculations, and at this time the direction of movement of electric charges is very meaningful.

2.Heat is a scalar quantity and temperature is a vector quantity. The temperature can be positive and negative!

Heat is actually energy, can energy be negative? Right? Generally, the direction of measuring a state is static, not a process, for example, when an object moves in a curve, it cannot explain its direction, but only in the direction of a certain time or place.

3.Velocity = displacement time. Time is a scalar quantity and displacement is a vector quantity, so velocity is a scalar quantity, and it is the same as displacement.

Circular motion is also known as uniform speed motion, do you understand this definition? High school will learn! That is, the velocity is varied, and it varies uniformly according to time, and it is not the magnitude of the force that changes, but the direction of the force.

That is to say, the velocity and displacement are variable at each moment, and when studying the displacement at a moment, the direction of movement and the direction of velocity are the same.

The current is a scalar quantity, but the current is directional (the vector is to follow the parallelogram rule) The current is generated by the directional movement of free electrons, and from the perspective of the circuit, the positive electrode flows to the negative electrode on the outside of the power supply, and the negative electrode flows to the positive electrode on the inside.

In the same way, heat is also a scalar quantity, it follows the law of parallelograms, and what you call direction is just a numerical increase or decrease.

The direction of velocity is the same as the direction of displacement, because displacement is also a vector quantity, and the direction of velocity is constantly changing when the object is moving in a circle, and the direction of displacement is actually constantly changing, which should be considered with the idea of limit. When doing circular motion, the direction of velocity points to the tangent direction of the circumference, which you should have learned when you learn circular motion.

1. The current has a direction and is a vector. The direction of the current is the same as the direction of the electric field, from the high potential to the low potential.

2. Heat is a scalar quantity, and heat is a manifestation of work, so it is a scalar quantity. The conduction of heat from a high-temperature place to a low-temperature place is actually a transfer of work. It is not the same as electric current, which is a manifestation of velocity.

3. It can only be said that the landlord does not read the book carefully, the direction of the speed is consistent with its movement trend, the force can change the magnitude of the speed can also change its direction, and the circular motion of the object is constantly affected by the force, so its speed direction is constantly changing. Judging the velocity direction of the object, not only the direction of displacement, but also its force state, only in the case of no force or equilibrium force, the displacement direction is consistent with the velocity direction, when considering the direction of movement of the particle, more often consider its motion trend.