Motion

Complutense University of Madrid

physics

Motion

Prof. J. Peña

UCM - Faculty of education

essentials of physics

contents

• Introduction
• Position & distance
• Reference systems
• Speed & Velocity
• Acceleration
• Activities

UCM - Faculty of education

essentials of physics

introduction

Motion is a fundamental concept in physics that explores the movement of objects and the factors influencing their motion. It involves the study of how objects change their position, velocity, and acceleration over time

Key concepts

Mind map

Vectors (video)

Kinematics (video)

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essentials of physics

position

Position is where an object is located. Always measured from a reference point, which is given a value of position = 0. When the object moves on a line we only need a reference point in order to know its position, whereas when it moves on a surface, we do need a Cartesian reference system.

Position is a “VECTOR” quantity. So, it has both a magnitude and a direction (+ or -)

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essentials of physics

distance

• Distance is a scalar quantity, so, it has no direction, just a magnitude (amount).
• For example, a car that runs around a 24 km long track runs a distance of 24 km.
• Distance means how far you go.

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displacement

• Displacement is a vector quantity.

• Displacement is the answer of the following question: What is your change in position from where you started?

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essentials of physics

reference system

• In physics, a reference system is a framework used to describe the motion and position of objects relative to a chosen point or set of axes.
• It provides a standardized way to measure and quantify physical quantities such as position, velocity, and acceleration.

Key concepts

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trajectory

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speed

How fast did you go?

• The rate at which you cover a distance.
• Measured in m/s.
• Mathematical definition: S=Distance/Time
• Is a ”SCALAR” quantity. Speed has no direction, only a magnitude.

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essentials of physics

velocity

How fast did you go and in which direction?

• Measured in m/s.
• Mathematical definition:

v=Displacement/Time

• Is a ”VECTOR” quantity. Velocity has both magnitude and direction.

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essentials of physics

instantaneous vs average

Instantaneous speed: how fast you are going at a given instant

The bike stopped to fill petrol

They arrived at the same time

Car and bike started together

The bike moved forward

The car continued its journey

Average speed: how fast you went on average over a given distance and time duration

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essentials of physics

constant speed motion

Every 2 seconds the man run 20 m, in other words, in equal time runs equal distance: motion is constant

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constant speed motion

Graphical analysis

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essentials of physics

acceleration

How quickly velocity changes?

At P0 the car is moving with velocity V0

• The rate of change of velocity.
• Measured in m/s2.
• Mathematical definition:

• Is a ”VECTOR” quantity.

At P the car is moving with velocity V

Acceleration is the rate of change of velocity.

Video

Graphical analysis

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essentials of physics

activities

1. Perform the graphycal analysis of the given data. Represent Distance versus time.(Time to 'x' axe and distances to 'y' axe).
2. Calculate the speed in cm/s, m/s and km/h.
3. Can you find any relation between velocity and the slope of time vs. distance? What type of motion do we have?
4. List possible causes of error.

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essentials of physics

activities

1. Perform the graphycal analysis of the given data. Bear in mind that time values to 'x' axe and distances to 'y' axe.
2. Evaluate the following statements: constant speed? Type of motion?
3. Calculate the acceleration? Final velocity?

• Discuss your results with your classmates...
• Compare findings: My results are similar to (or different from) those of my classmates in that...
• Think about what you found out. How does it fit with what you already knew? How does it change what you thought you knew? My ideas have changed from the beginning of this activity because of this evidence... My ideas changed in the following ways... One concept I still do not understand involves...
• One part of this activity I am most proud of is...

• Discuss your results with your classmates...
• Compare findings: My results are similar to (or different from) those of my classmates in that...
• Think about what you found out. How does it fit with what you already knew? How does it change what you thought you knew? My ideas have changed from the beginning of this activity because of this evidence... My ideas changed in the following ways... One concept I still do not understand involves...
• One part of this activity I am most proud of is...

• Position refers to the location of an object in relation to a reference point or coordinate system. It is commonly described using distance and direction.
• Displacement is a vector quantity that measures the change in position of an object from its initial position to its final position. It takes into account both the distance and direction of the movement.
• Velocity is a vector quantity that describes the rate at which an object changes its position. It is defined as the displacement per unit time and includes both magnitude (speed) and direction. Velocity can be constant or varying depending on the object's motion.
• Speed is a scalar quantity that represents how fast an object is moving. Unlike velocity, speed does not consider the direction of motion and is calculated as the distance traveled per unit time.
• Acceleration is the rate of change of velocity. It measures how quickly an object's velocity is changing. Acceleration can be positive (speeding up), negative (slowing down), or zero (constant velocity). It is also a vector quantity, taking into account both magnitude and direction.
• Kinematic equations are mathematical formulas that relate the variables of motion, such as displacement, velocity, acceleration, and time. These equations allow us to calculate unknown quantities given known values.

• The origin is a fixed point within the reference system that serves as the starting point for measuring positions. It is often denoted as the coordinate (0,0,0) and acts as a reference point for all other measurements.
• The axes are imaginary lines or directions that extend from the origin in different directions. They provide a means to define spatial dimensions and measure distances. In a three-dimensional reference system, there are typically three axes: x, y, and z, representing the horizontal, vertical, and depth dimensions, respectively.
• The reference system requires units of measurement for quantities such as distance, time, and mass. These units establish a standardized scale for measurements and ensure consistency in calculations.