Physics 8 Lesson 1: Mechanical movement
1. Theoretical summary
1.1. Mechanical movement
The change in position of an object over time relative to another object (the landmark) is called mechanical motion (referred to as motion).
An object is said to be at rest when its position does not change over time relative to another object.
Eg: The train leaves the station, the position of the train changes relative to the station, we say the train is moving relative to the station
1.2. The movement relative
An object may be considered to be in motion relative to one object, but considered to be at rest relative to another. We say motion or rest is relative, depending on the object chosen as a landmark.
Usually people choose the Earth or objects associated with the Earth as landmarks (houses, trees, vehicles, lampposts, etc.)
1.3. Common types of movement
The path drawn by a moving object is called the trajectory of the motion.
– Depending on the shape of the orbit, we divide the motion types:
Attention: The movement trajectory of the bicycle valve head is both curved relative to the wheel axis, and along with the bicycle moving straight on the road.
1.4. Solution method
a) How to tell if an object is moving or at rest?
– When we say that an object is moving or at rest, what is the reference to the reference object? To know whether object A is moving or at rest relative to object B, we must consider the position of object A relative to object B.
If the position of object A relative to object B changes with time, then object A is said to be in motion relative to object B.
If the position of object A relative to object B does not change with time, then object A is said to be at rest relative to object B.
b) Relativity of motion
To prove that motion or rest is relative, we must choose at least three objects: Object 1, object 2, object 3 such that object 1 is moving relative to object 2 but is at rest relative to object 3.
2. Illustrated exercise
2.1. Form 1: Determine the position of the object
Passengers on train A see train B moving forward. Passengers on train B saw train C moving forward as well. So passengers on train A will see train C
Passengers on train A will see trains B and C moving forward in the same direction.
2.2. Type 2: Explain the relativity of motion and rest
Explain why motion and rest are relative.
Motion and rest are relative because an object can be at rest relative to one object but be in motion relative to another.
3.1. Essay exercises
Question 1: What is the movement of the bicycle valve head relative to the wheel axis when the vehicle is moving straight on the road?
Verse 2: It’s quiet, looking through the car window (when the car is stationary) we see raindrops falling in a vertical line. If the car moves forward, how will the people sitting in the car see the raindrops moving?
Question 3: Is the change in the path of the light ray from the air to the water mechanical motion? Why?
Question 4: A passenger car runs on the road, the co-driver checks the tickets of the passengers on the car. If the driver is chosen as a landmark, is the car stationary or moving?
3.2. Multiple choice exercises
Question 1: Which of the following statements is true regarding mechanical motion?
A. Mechanical motion is the movement of an object.
B. Mechanical motion is the change in position of one object relative to another over time.
C. Mechanical motion is the change in velocity of an object.
D. Mechanical motion is the displacement of an object’s position.
Verse 2: Observing a train coming into the station, which of the following descriptions is false?
A. The train is moving relative to the station.
B. The train is at rest relative to the driver.
C. The train is in motion relative to the passengers sitting on the train.
D. The train is moving relative to the passenger standing under the platform.
Question 3: The trajectory of an object’s motion is
A. the line traced by a moving object in space.
B. a straight line of a moving object drawn in space.
C. the circle of a moving object traced in space.
D. the curve of a moving object outlined in space.
Question 4: The sun rises in the east, sets in the west. In this phenomenon:
A. The Sun moves and the Earth is stationary.
B. The Sun is stationary and the Earth moves.
C. The Sun and Earth both move.
D. The Sun and Earth are both stationary.
Through the lecture Mechanical movement Here, you need to accomplish some of the goals that the lesson gives, such as:
- Give examples of the relativity of motion and rest, especially knowing how to determine the state of an object for each object chosen as a landmark.
- Give examples of mechanical motion in everyday life.
- Give examples of common types of mechanical motion: linear motion, curvilinear motion, and circular motion.