Acceleration and friction
Publish: 2021-05-19 18:29:10
1. The contact point with the ground is only the instantaneous center of velocity, but not the instantaneous center of acceleration. Yes, but it does not contradict the law. Because the rotation equation is established for the instantaneous center of velocity, but not for the instantaneous center of acceleration. Therefore, the first method is correct< In the second method, it is obviously groundless to say that if there is no sliding, then the friction force is equal to f = 24N. There is only one non slip: the relative velocity is 0, which has nothing to do with the moment balance. And even if the friction force is used to balance, the acceleration should be (24 + 24) / 8 = 6
2. Acceleration, i.e; A physical quantity that describes the speed and direction of an object. If the speed of an object changes greatly and takes a short time, the speed changes quickly, that is, the acceleration is large, and vice versa. It can be seen that the acceleration is the rate of change of speed with respect to time. Unit: M / S2
definition of acceleration a= Δ v/ Δ T
definition of friction force: if two objects in contact with each other move relatively or tend to move relatively, a force hindering the relative motion will be generated on the contact surface of the two objects, which is called friction force, If two objects in contact have relative sliding, the force in contact is called sliding friction. The size of friction is related to the material of the contact surface and the smoothness of the surface, as well as the positive pressure between objects, First, we should judge whether the friction is sliding friction or static friction, and then calculate it by corresponding methods.
the calculation formula of sliding friction is f= μ N, where μ Dynamic friction coefficient, also called sliding friction coefficient, is only related to material and roughness of contact surface, but has nothing to do with contact area; N is the positive pressure
definition of acceleration a= Δ v/ Δ T
definition of friction force: if two objects in contact with each other move relatively or tend to move relatively, a force hindering the relative motion will be generated on the contact surface of the two objects, which is called friction force, If two objects in contact have relative sliding, the force in contact is called sliding friction. The size of friction is related to the material of the contact surface and the smoothness of the surface, as well as the positive pressure between objects, First, we should judge whether the friction is sliding friction or static friction, and then calculate it by corresponding methods.
the calculation formula of sliding friction is f= μ N, where μ Dynamic friction coefficient, also called sliding friction coefficient, is only related to material and roughness of contact surface, but has nothing to do with contact area; N is the positive pressure
3. In order to establish the relationship between acceleration and friction, we need the help of F = M × a Acceleration is a measure of how fast an object's original state changes, while friction is the contact force between two objects. The relationship between them can only be discussed under special conditions.
4. (1)
think that the object is subject to dynamic friction
so:
friction: F = MGU = 1kg * 10m / (s ^ 2) * 0.2 = 2n
tension: F = 5N
resultant force: F (combination) = f-f = 5n-2n = 3N
acceleration: a = f (combination) / M = 3N / 1kg = 3m / (s ^ 2)
because the initial velocity is 0
so s = 1 / 2at ^ 2 = 0.5 * 3m / (s ^ 2) * 4 ^ 2S = 24m
think that the object is subject to dynamic friction
so:
friction: F = MGU = 1kg * 10m / (s ^ 2) * 0.2 = 2n
tension: F = 5N
resultant force: F (combination) = f-f = 5n-2n = 3N
acceleration: a = f (combination) / M = 3N / 1kg = 3m / (s ^ 2)
because the initial velocity is 0
so s = 1 / 2at ^ 2 = 0.5 * 3m / (s ^ 2) * 4 ^ 2S = 24m
5. Let the acceleration of object B be y, then the friction force = B (kg) x (9.8-y)
or friction = B (pressure) x friction coefficient
or friction = B (pressure) x friction coefficient
6. If there's friction, of course.
7. Because of the uniform acceleration motion, vt-v0 / T = a, a = 2
f-f = ma
F can also be calculated
in UMG = f
it is completed
f-f = ma
F can also be calculated
in UMG = f
it is completed
8. f = ma
f = 2.5 × 2
= 5N
the direction of F is opposite to the initial velocity of the object.
f = 2.5 × 2
= 5N
the direction of F is opposite to the initial velocity of the object.
9. Because the board is still, the friction force of people to the board is upward along the inclined plane, which is set as F,
and satisfies: F = m0gsin θ
because the friction force between people and the board goes up along the slope, people speed up to run down, and the friction force between the board and people goes down along the slope
for people: mgsin θ + F = ma,
the solution is a = (M0 + m) GSIN θ/ m
and satisfies: F = m0gsin θ
because the friction force between people and the board goes up along the slope, people speed up to run down, and the friction force between the board and people goes down along the slope
for people: mgsin θ + F = ma,
the solution is a = (M0 + m) GSIN θ/ m
10. The direction of supporting force is always perpendicular to and upward of the surface you step on, while the direction of gravity is always perpendicular to the ground. As long as there is a slope, there is an angle between gravity and the surface you step on, and gravity will proce component forces in the direction of
along the surface and
perpendicular to the surface, And the component force of gravity
perpendicular to the surface is always equal to the supporting force, and the direction is opposite, while the force along the surface must be downward along the direction of the surface. When the object slides up the slope, the direction of friction is downward. When it slides down the slope, the direction of friction is upward; You want to go down, it prevents you from going down, and it goes up at this point). Whether it is uphill or downhill, acceleration is composed of gravity component along the slope + friction, the difference is the direction. When sliding upward, the component force of gravity is downward along the inclined plane, and the friction force is downward
when sliding down, the force component of gravity is downward along the inclined plane, and the friction force is upward.
along the surface and
perpendicular to the surface, And the component force of gravity
perpendicular to the surface is always equal to the supporting force, and the direction is opposite, while the force along the surface must be downward along the direction of the surface. When the object slides up the slope, the direction of friction is downward. When it slides down the slope, the direction of friction is upward; You want to go down, it prevents you from going down, and it goes up at this point). Whether it is uphill or downhill, acceleration is composed of gravity component along the slope + friction, the difference is the direction. When sliding upward, the component force of gravity is downward along the inclined plane, and the friction force is downward
when sliding down, the force component of gravity is downward along the inclined plane, and the friction force is upward.
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