Frank
Hello, this is Frank.
Starting today, I’ll begin reviewing high school physics using the reference book “Mou Ichido Koukō Butsuri” (High School Physics Once Again).
As someone who struggles with physics, I’ll stick closely to the structure of the textbook while breaking things down in simpler terms—thanks for your understanding.
The book I ordered arrived in good condition, and the explanations are large-print and beginner-friendly, which is perfect for someone like me. I plan to study it alongside my sister site, Experts at Mathematics.
Let’s start with the forces that act on objects in high school physics. A force causes a change in an object’s state of motion, and it can be classified as follows:
1. Types of Forces Acting on Objects
1) Field Forces
These are forces that act without physical contact, such as gravity, electric forces, and magnetic forces:
- Gravity: The force pulling objects toward Earth. Near the Earth’s surface, the gravitational force is F = mg, where g ≈ 9.8 m/s².
- Electric Force: A charged particle in an electric field E experiences a force F = qE.
- Magnetic Force: A moving charge q with velocity v in a magnetic field B experiences a force F = q(v×B).
2) Contact Forces
These are forces that require direct contact, such as friction and normal forces:
- Normal Force: The force exerted by a surface perpendicular to an object resting on it.
- Friction: The force that resists sliding motion between surfaces, which includes static, maximum static, and kinetic friction.
2. Types of Contact Forces
1) Normal Force:
This is the perpendicular force exerted by a surface on an object in contact with it, such as a book resting on a table.
2) Frictional Forces:
There are three types:
- Static Friction: The force that prevents an object from starting to move. It increases up to a maximum point.
- Maximum Static Friction: The force at the moment an object begins to move. It is given by Fₛ = μₛN.
- Kinetic Friction: The constant force acting after movement begins. It is given by Fₖ = μₖN.
3. Inertial Force
Inertial force appears in non-inertial reference frames (those with acceleration). For example, when a car brakes suddenly, the forward force you feel is an inertial force.
In conclusion, forces are divided into field forces (acting without contact) and contact forces (requiring contact). Contact forces include the normal force and friction, and friction can be broken down into static, maximum static, and kinetic types.
Understanding these forces is essential for analyzing motion and force balance.
Here’s a set of problems for those who’ve completed the basics of mechanics. Answers follow at the end.
【Practice Questions】
A 2 kg object is pulled along a frictionless horizontal surface with a constant force of F = 10 N. The object starts from rest and its motion is analyzed at three points:
- Find the velocity at t = 2 seconds after the force is applied.
- The object hits a smooth wall, producing a normal force N. Calculate N, assuming horizontal velocity remains unchanged upon impact.
- While in continuous contact with the wall, assuming constant acceleration a, explain how the inertial force fi acts on the object.
【Reference Book】
“Mou Ichido Koukō Butsuri” by Kazuhiko Tamechika, Nihon Jitsugyo Publishing
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【Disclaimer】
While we strive for accuracy and timeliness, we cannot guarantee the completeness of this content. We are not responsible for any errors related to this content.
【Gratitude】
Special thanks to Pixabay for free images, and to ChatGPT for generating the initial draft, which I revised and commented on during my study of the reference material.
【Copyright】
All text rights are retained by the original author and OpenAI. Reproduction or reuse must cite the source.
【Model Answers】
- Velocity at t = 2 seconds:
Using Newton’s second law: F = ma → a = F/m = 10/2 = 5 m/s²
Since initial velocity v₀ = 0:
v = v₀ + at = 0 + (5 × 2) = 10 m/s - Normal force N:
When the object hits a smooth wall, it experiences a normal (reaction) force perpendicular to the wall. Since the wall does not change the horizontal motion, and no vertical force is applied, N = 0 N in this simplified model. - Inertial force fi:
In a non-inertial frame (accelerating reference), an apparent force appears in the direction opposite the acceleration:
fi = −ma = −(2 kg × 5 m/s²) = −10 N
Thus, the inertial force acts with 10 N magnitude in the direction opposite to the motion.
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