Multivariable Calculus · 免费预览

三重积、力矩与体积

标量三重积作为行列式与体积、向量三重积,以及叉积在力矩与转动中的应用。

1. The scalar triple product packages volume into one determinant

The scalar triple product packages volume into one determinant

2. The sign of the triple product records orientation

The sign of the triple product records orientation

3. Torque is the cross product of the lever arm with the force

Torque is the cross product of the lever arm with the force

4. Rotation of a rigid body brings the pieces together

Rotation of a rigid body brings the pieces together

5. Computing a scalar triple product

Let a=(2,0,0)\mathbf{a} = (2, 0, 0), b=(1,3,0)\mathbf{b} = (1, 3, 0) and c=(0,1,4)\mathbf{c} = (0, 1, 4). What is the value of a⋅(b×c)\mathbf{a} \cdot (\mathbf{b} \times \mathbf{c})?

6. Volume of a parallelepiped

Three edge vectors from one corner of a parallelepiped are (1,0,0)(1, 0, 0), (0,2,0)(0, 2, 0) and (1,1,3)(1, 1, 3). What is the volume of the solid they span?

7. Torque from a lever arm and a force

A mechanic pulls a wrench with force F=(0,20,0)\mathbf{F} = (0, 20, 0) newtons at the point r=(0.5,0,0)\mathbf{r} = (0.5, 0, 0) meters from the bolt. What is the torque about the bolt?

8. Reading the sign of a triple product

Three vectors satisfy a⋅(b×c)=−7\mathbf{a} \cdot (\mathbf{b} \times \mathbf{c}) = -7. What does the sign tell you about the ordered triple (a,b,c)(\mathbf{a}, \mathbf{b}, \mathbf{c})?

9. Volume of a tetrahedron from three edges

Three edge vectors from one vertex of a tetrahedron are (2,0,0)(2, 0, 0), (0,3,0)(0, 3, 0) and (0,0,6)(0, 0, 6). The tetrahedron's volume is a fixed fraction of the parallelepiped volume. Give the tetrahedron volume as a number.

10. A missing height component

A parallelepiped has edge vectors (1,0,0)(1, 0, 0), (0,2,0)(0, 2, 0) and (0,1,h)(0, 1, h), and its volume is 44. Give the value of hh.

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