摩擦类型——定义、静态、动力学、滚动和流体摩擦
摩擦力几乎存在于物理世界的各个方面。这些力相互对抗物体的运动。这样,它们既负责运动又抵抗运动。产生这些力的主要原因是由于粘附。粘附力是不同物体之间的吸引力。由于这种力,很难将不同的物体相互摩擦,并且会产生抵抗这种运动的力。这称为摩擦。让我们详细看看这些力量。
摩擦
摩擦力可以定义为在两个接触并相互滑动的表面之间产生的力。这些力取决于纹理和施加在它们上的力以使它们相互滑动。由于表面的不规则性而产生摩擦。跨越这些不规则的剪切会产生这种力,这会使运动更加困难。
如果一个物体简单地放在另一个物体上并移动,摩擦力就是物体的重量。当两个物体之间表面上的法向力开始增加时,摩擦力也开始增加。这意味着摩擦取决于表面之间的法向力。表面可以施加的最大力由下式给出,
F = μF范数
上面提到的μ称为摩擦系数。它的值介于0和1之间。物体静止时作用在物体上的摩擦力称为静摩擦力,而运动时作用在物体上的摩擦力称为动摩擦力。
摩擦类型
摩擦力是一种抵抗任何两个物体之间运动的力。根据摩擦力的性质和作用的材料,摩擦力可以分为多个类别。某些摩擦仅作用于固体,而其他摩擦作用于气体和液体。所有这些摩擦都可以进一步细分和细分。摩擦可分为以下子类别:
- 干摩擦
- 静摩擦力
- 动摩擦
- 滚动摩擦
- 流体摩擦
干摩擦
干摩擦通常在固体表面之间起作用。这种摩擦总是与两个表面之间的运动相反。这种摩擦也称为库仑摩擦。这种摩擦又可以分为静摩擦和动摩擦两种。下图表示当对盒子施加力以移动盒子时作用在盒子上的摩擦力。力会增加,直到盒子开始移动。
Static Friction — This friction before the box starts moving. In this case, the friction is equal to the force applied. As the applied force increases, so does the friction. If the force keeps on increasing, the friction also increases, but there comes a point when the box starts moving. The point just before the box slips is called impeding motion. At this point, the static friction is maximum. It is determined by the coefficient of static friction
Formula for static friction
Kinetic Friction — Kinetic friction starts acting when the box starts moving. Its value is less than the maximum static friction. In this case, no matter what the applied force is, the value of the kinetic friction will remain the same. In this case, it is determined by the coefficient of kinetic friction
Formula for Kinetic friction:
Rolling Friction — This happens when a disc or ball rolls over a surface. The reason for this seems to be the distribution of energy involved in the twisting of objects. The coefficient used for the Rolling friction is determined as Crr and is known as Dimensionless rolling resistance coefficient.
Formula for Rolling friction:
F= Crr N
Examples — basketball rolling on the floor, painting the walls using paint rollers, ball bearing (as shown in the figure above).
流体摩擦
该函数发生在彼此相对移动的流体层之间。这种摩擦是流动的内部摩擦,也称为粘度。几乎所有的流体都表现出对剪切的抵抗力,因此是粘性的。在空中飞行的飞机会受到阻力。这种阻力是由于空气的粘性造成的。另一个例子是跳伞时降落伞减速。
流体摩擦公式:
A=面积
=层的速度之间的差异
板间距
示例问题
问题 1:在地面上放置一个 4Kg 的积木,施加 60N 的力。如果静摩擦系数由下式给出,则求静摩擦的极限值, μ s =0.4。
回答:
The formula for limiting static friction is given by,
Normal Force N = 60 + 4(10) = 100 N
Plugging in the values in the equation,
⇒ F = (0.4)(100)
⇒ F = 40N
问题2:地上放着一块4Kg的积木。如果静摩擦系数由下式给出,则求静摩擦的极限值, μ s =0.2。
回答:
The formula for limiting static friction is given by,
Normal Force N = 4(10) = 40 N
Plugging in the values in the equation,
⇒ F = (0.2)(40)
⇒ F = 8 N
问题3:地上放着一块4Kg的积木。水平施加 100N 的力,动摩擦系数由下式给出, 求块的加速度。
回答:
The formula for limiting static friction is given by,
Normal Force N = 4(10) = 40 N
Plugging in the values in the equation,
⇒ F = (0.2)(40)
⇒ F = 8 N
The kinetic friction will be, 8 N.
Net resultant force = 100 – 8
= 92 N
F = ma
⇒ 92 = 4(a)
⇒ 23 m/s2 = a
问题4:地上放着一块5Kg的积木。水平施加 10N 的力,动摩擦系数由下式给出, μ s =0.1。求块的加速度。
回答:
The formula for limiting static friction is given by,
Normal Force N = 5(10) = 50 N
Plugging in the values in the equation,
⇒ F = (0.1)(50)
⇒ F = 5 N
The kinetic friction will be, 5 N.
Net resultant force = 10 – 5
= 5 N
F = ma
⇒ 5 = 5(a)
⇒ 1 m/s2 = a
问题4:地上放着一块5Kg的积木。水平施加 10N 的力,动摩擦系数由下式给出, .找到加速度。
回答:
The formula for limiting static friction is given by,
Normal Force N = 5(10) = 50 N
Plugging in the values in the equation,
⇒ F = (0.1)(50)
⇒ F = 5 N
The kinetic friction will be, 5 N.
Net resultant force = 10 – 5
= 5 N
F = ma
⇒ 5 = 5(a)
⇒ a= 1 m/sec2