In physics, how to find out whether a small wooden block on an inclined plane will slide down?

Analysis: (Analysis of the situation where the velocity of the block is 0 when it is originally placed) If the block of mass m is placed on a rough slope with an inclination angle of .

, the dynamic friction factor between the block and the inclined plane.

For the wood block is subjected to gravity mg, support force n, friction force on the inclined plane.

f (up along the inclined plane).

Gravity is orthogonally decomposed.

In the direction of the parallel inclined plane and the perpendicular inclined plane, then.

The component in the parallel inclined direction is g1 mg * sin The component in the perpendicular inclined direction is g2 mg * cos Since it is impossible for the block to leave the inclined plane, there is n g2 mg * cos If mg * sin mg * cos, the block will slide down (corresponding to tan).

If mg * sin mg * cos, the block will not slide down (corresponding to tan).

Orthogonally decomposes the gravity of the block, breaking it down into a pressure perpendicular to the inclined plane and a force down the inclined plane. Pressure*Friction is calculated to calculate the maximum static friction, if the gravity component along the inclined face is greater than the maximum static friction, it will slide down, otherwise it will not.

When tan, the small wooden block will slide down, and when tan, the small wooden block will not slide down (for the east friction factor of the inclined plane, for the angle of the inclined plane).

No, it's the gravitational component that is greater than the frictional force.

Gravity is greater than friction.

mgsinθ=f

f=mgsinθ+f

From the above two formulas, it can be obtained:

f=2mgsinθ

Answer: (1) Objects and inclined planes.

The dynamic friction is mgsin;

2) Keeping the inclination angle constant, in order for the object to slide up at a uniform speed, the thrust is 2mgsin

At 45 degrees, the block accelerates its slide, and the friction of the block at 30 degrees and 45 degrees is equal, so 30 degrees is the critical angle, and the friction is equal to the component of gravity, <

tan30° 。The root number 2 is tan45°, but at 45 degrees the block has accelerated its downward slide, and the component of gravity is not equal to friction, so it is not equal to tan45°, and tan30° is correct.

The most important way to solve this kind of physics problem is to analyze the force on the object.

Analyze the forces on the wooden block, subject to gravity and inclined planes.

The direction of the supporting force g is vertically downward, and the direction of the supporting force n is perpendicular to the inclined plane.

Let the angle of the inclined plane be , decompose n as the horizontal direction nsin, the vertical direction ncos, and the net force in the vertical direction is 0, that is, ncos g, and the component nsin the horizontal direction is to cause the wood block to produce acceleration.

The reason, i.e., nsin ma, is that the inclined plane is the object of force and the wooden block is the object of force, and both act by pressure n.

This kind of question has a pattern, the most important is the force analysis, select the object to be analyzed, carefully investigate its force, be careful not to add or miss the force, each force must be able to find the force object.

OK. Imagine that.

When there are raindrops on the glass of a car traveling at high speed...

The rain will go up along the car glass.

Instead of sliding down.

It's the same principle as this.

The gravitational force of an object is a resultant force.

His share of strength.

One branch is the downward component.

So if the inclined plane does not move.

The object slides (provided that the sliding friction is less than the gliding component) and when the inclined plane moves with a certain acceleration.

That is, there is a thrust force on the object in the direction of acceleration (the acceleration of the object must be less than or equal to the acceleration of the inclined plane).

At this time, the wooden block is in the case of using the inclined plane as a reference.

That is, it is moving in the opposite direction or not moving.

And because of the inertia of the object.

So the object may be stationary or it may be moving upwards along an inclined plane.

He was given the support of the inclined plane.

This force gives the same acceleration in the horizontal direction as the inclined plane, so it is relatively stationary, and the vertical direction is balanced with gravity.

The wooden block is subjected to the gravitational force g exerted by the earth, the direction is vertically downward, and it is also subjected to the supporting force f exerted by the inclined plane, the direction is perpendicular to the contact surface upwards, and it is also subjected to the frictional force f of the inclined surface on the wooden block, and the gravity, support force, and frictional force work together to make the wooden block slide, in fact, there is no single sliding force The diagram is as follows:

Gravity over the center of gravity is used vertically downward, and gravity is used along the inclined plane over the center of gravity.

Upward friction of the wheel.

The fulcrum is used to support the upward perpendicular to the inclined face of the Tongnian as shown in the diagram

Unchanged decreases and increases.

In the process of sliding down the wooden block, the elastic deformation of the wooden block does not occur, and the potential energy of the elastic selling cover is not considered In the process of placing and selling the wooden block under the wooden block, the mass of the wooden block remains unchanged, the speed does not change, the kinetic energy does not change, the height decreases, and the gravitational potential energy decreases

In the process of sliding down the wooden block, there is friction between the wooden block and the inclined plane excavation, and the mechanical energy is converted into internal energy and the internal energy is increased by overcoming the friction and doing work

So the answer is: unchanged; Minish; Enlarged