Name: using vectors to describe motion
Uploaded: 2023-09-22T11:49:39.000Z
Duration: 1 min
Channel: JoVE

考虑一只运动中的果蝇。为了确定其在三维空间中的位置，使用笛卡尔坐标系，而沿各轴的单位向量则提供了其方向。
从原点延伸至物体位置的矢量箭头称为位置矢量。它可以用单位矢量来表示。
位置矢量是各坐标轴上矢量分量的总和，其大小表示沿各坐标轴的位置。
如果果蝇持续运动，其位置矢量会发生变化，位置矢量之间的矢量差称为位移矢量 Δr，它表示位置的变化。
例如，如果果蝇位于点 A，经过时间 t 后到达点 B，则利用点 A 和点 B 的位置矢量，可求得果蝇在时间 t 内的位移矢量。

位置与位移矢量

Position and Displacement Vectors

要描述一个物体的运动，首先应该能够描述它的位置，即它在任何特定时刻的位置。 更准确地说，必须相对于一个合适的参考系来确定其位置。 参考系是一组任意选择的坐标轴，用来描述物体的位置和运动。 地球通常用作参考系来描述物体相对于地球上另一个静止物体的位置。
此外，几种重要的运动发生在二维中，也就是在平面上。 这些运动可以用位置、速度和加速度的两个分量来描述。 如果一个物体相对于参考系发生运动，其位置就会改变； 这种位置的变化称为位移。 位移一词意味着物体已发生移动或或被移动。 由于位移具有方向性，因此它是一个矢量，可以是正值，也可以是负值，具体取决于方向的选择。 此外，运动分析往往涉及多个位移，而在物理学的许多应用中，也存在一系列位移。 因此，总位移等于各个位移的总和，需要用矢量加法仔细计算。

 本文改编自 <a href="https://openstax.org/books/university-physics-volume-1/pages/4-1-displacement-and-velocity-vectors">Openstax，大学物理第 1 卷，第 4.1 节：位移和速度矢量。</a>

要描述一个物体的运动，首先需要能够描述其位置（即在任意特定时刻它所处的位置）。更准确地说，位置……

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教育

JoVE Core

Mechanical Engineering

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Unit 1

第一单元

Physics Basics

物理基础

KEY TERMS AND CONCEPTS

关键术语与概念

位置和位移矢量

using vectors to describe motion

Position and displacement vectors describe motion in physics. A position vector shows where an object is located relative to a chosen origin. A displacement vector shows how far and in what direction the object moves from one point to another.

These vectors are useful because they give a clear way to track movement in space. The video connects position and displacement to the idea of a reference point and shows how direction matters as much as distance. That makes them important for describing motion in one, two, or three dimensions.

The lesson also shows how to represent these vectors using arrows and coordinate systems. By comparing the starting point and ending point, students can see the difference between an object’s location and its change in position. This helps build the foundation for later topics in kinematics.

Using Vectors to Describe Motion

introduction to scalers

Scalar Quantities in Physics

Scalar quantities in physics have size only. They do not include direction. This makes them different from vector quantities. Common scalar examples include mass, temperature, time, and energy. Each one can be described with a number and a unit. Because direction is not part of the value, scalars are often easier to compare and measure.

vector or cross product

Cross Product of Two Vectors

The cross product of two vectors gives a new vector that is related to both original vectors. It is also called the vector product. In many physics problems, this operation helps describe quantities that depend on direction as well as size. The result of a cross product has a direction set by the two input vectors. It is not the same as ordinary multiplication. The transcript focuses on the vector or cross product as a core vector operation students use when working with vectors in science.

introduction to vectors

Vectors in Motion and Direction

Vectors describe quantities that have both size and direction. They are used in physics to show how motion, force, and other quantities act in space. A vector can be represented with an arrow. The length of the arrow shows the size, and the arrowhead shows the direction. This makes vectors useful for comparing how one quantity points relative to another. Scalars are different because they have size only and no direction. Understanding the difference between vectors and scalars is an important...

units and standards of measurement

Measurement Units, Standards, and SI Basics

Measurement units, standards, and SI basics help scientists describe physical quantities clearly. A unit gives a number meaning, while a standard provides a fixed reference for that measurement. Together, they make results easier to compare and understand. The International System of Units, or SI, is the most common measurement system in science. It uses agreed-upon base units for common quantities. These standards reduce confusion when measurements are shared across labs, classrooms, and...

accuracy and precision

Measurement Errors, Accuracy, and Precision

Measurement errors can affect how close a result is to the true value and how consistent repeated results are. Accuracy describes how close a measurement is to the accepted or true value. Precision describes how close repeated measurements are to one another. A result can be accurate, precise, both, or neither. A set of measurements may cluster tightly together and still be far from the true value. Another set may include values spread out from one another, even if one of them is close to the...

rules of significant figures

Counting Significant Figures in Measurements

Significant figures help students record measurements with the correct level of precision. They show which digits in a number are meaningful and which only help place the decimal point. In science class, this idea matters when writing and comparing measured values. The rules for significant figures explain how to count these digits in different numbers. Some digits are always counted, while others depend on where they appear in the number. Learning the rules makes it easier to report answers...

random and systematic errors

Measuring Error in Scientific Data

Random and systematic errors affect scientific measurements. Random errors cause values to spread around the true value. They make repeated measurements less consistent. Systematic errors shift measurements in the same direction each time. Understanding both kinds of error helps students judge data quality. Random error can come from small changes during measurement. Systematic error can come from a biased tool or method. Scientists look for these patterns so they can improve results and...

position and displacement

Tracking Motion with Position and Displacement

Position and displacement are key ideas in straight-line motion. Position tells where an object is located compared with a chosen starting point, called the origin. Displacement describes how far and in what direction the object has moved from its starting position. These ideas help describe motion clearly. Position can change as an object moves. Displacement focuses on the change in position, not just the path taken. That makes it useful for comparing motion in a simple and precise way.

position and displacement vectors

Position and displacement vectors describe motion in physics. A position vector shows where an object is located relative to a chosen origin. A displacement vector shows how far and in what direction the object moves from one point to another. These vectors are useful because they give a clear way to track movement in space. The video connects position and displacement to the idea of a reference point and shows how direction matters as much as distance. That makes them important for describing...

mass and weight

How Mass Differs from Weight

Mass and weight are related, but they are not the same. Mass is the amount of matter in an object. Weight is the force of gravity acting on that object. This difference matters because mass stays the same even when gravity changes. Weight can change if the gravitational pull changes. A person or object therefore has the same mass, but not always the same weight. The terms are often used in everyday speech as if they mean the same thing. In physics, they describe two different ideas.

acceleration due to gravity on earth

Free-Fall Acceleration on Earth

Free-fall acceleration on Earth describes how fast an object speeds up when gravity is the only force acting on it. Near Earth’s surface, this acceleration is nearly constant for many everyday situations. Gravity pulls objects toward Earth and gives them downward acceleration. This motion is often written as g, and it helps explain why falling objects gain speed as they move downward. The value of g is commonly used in physics to predict the motion of objects dropped or released near the...

tension

Tension in Ropes and Strings

Tension is the pulling force carried by a rope, string, or cable when it is stretched by a load. In physics, this force acts along the length of the object and pulls away from the objects at each end. A stretched rope can support a hanging mass because the tension in the rope balances the weight of the load. The same idea appears in many everyday situations, such as a cable holding a sign or a string lifting an object. Understanding tension helps students connect force diagrams to real motion.

gravitational force

How Gravity Acts Between Objects

Gravity is a force that pulls objects toward one another. On Earth, this force gives objects weight and keeps people, water, and other materials from drifting away. It also helps explain why planets and moons stay in motion around larger bodies. The strength of gravitational force depends on the masses of the objects involved. Larger masses create a stronger pull, while smaller masses create a weaker one. The distance between objects also matters, because gravity becomes weaker as objects move...

key terms and concepts

Learn how position vectors and displacement vectors describe an object’s location and movement in 1D, 2D, and 3D using arrows and coordinates.

Using Vectors to Describe Motion | JoVE K12

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Using Vectors to Describe Motion

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