Fix the mistake: Force and Pressure

The Effects of Forces and How to Represent Them

The effect that moves, stops, or changes the shape of an object is called a force. Let us learn how to represent invisible forces with arrows.

Basic Knowledge

Forces have three effects:
① Change the shape of an object (stretching a spring, pressing clay)
② Change the state of motion of an object (moving a stationary object, stopping a moving object)
③ Support an object (a desk supporting a book)
The unit of force is N (newton). 1N is approximately equal to the gravitational force acting on a 100g object (on Earth).
A force has three elements: magnitude, direction, and point of application, and is represented by an arrow (vector). The length of the arrow represents magnitude, its direction represents the direction of the force, and its starting point represents the point of application.

Important Terms
Force (a cause that changes an object's motion or shape. Measured in N)
Newton (N) (the unit of force. The gravitational force on a 100g object ≒ 1N )
Three elements of force (magnitude・direction・point of application)
Point of application (the point at which a force acts. The starting point of the arrow)
Elastic force (the force by which a deformed object tries to return to its original shape. Springs・rubber)
Frictional force (a force that acts at a contact surface in the direction that obstructs motion)

Further Exploration (Background and Significance)

Forces around us can be classified into several types:
・Gravitational force (the force with which Earth attracts objects, discussed in detail later)
・Normal force (the force with which a surface pushes an object back)
・Frictional force (the force that obstructs motion at a contact surface)
・Elastic force (the restoring force of springs and rubber)
・Tension (the force with which a string pulls)
・Magnetic and electric forces (forces produced by magnets and electricity)
These forces can be classified according to whether they act without contact (gravitational, magnetic, and electric forces) or arise through contact (friction, elastic force, and tension).
The unit of force, N, comes from Newton, one of the fathers of modern physics. 1 N = 1 kg・m/s² is defined as “the force that gives a 1kg object an acceleration of 1m/s²” (studied in greater detail in the third year of middle school).

Key Points
  • Three effects of force: shape・motion・support
  • The unit of force is N (newton)
  • The gravitational force on a 100g object ≒ 1N
  • Forces are represented by arrows (vectors)
  • Three elements of force: magnitude・direction・point of application
  • Contact forces (friction・elastic force・tension) and non-contact forces (gravity・magnetic force)
  • The force of a spring = elastic force

Points to Note (Easily Confused)

① Mass (kg) and weight (N) are different concepts. Mass is the amount of matter, while weight is the force with which Earth attracts an object. ② When drawing a force, do not draw only the arrow; pay attention to the point of application (the starting point). ③ Elastic force is the force that tries to restore the original shape. It does not continue to occur no matter how far a spring is stretched; there is an elastic limit. ④ Frictional force acts in the direction that obstructs motion (opposite to the direction of movement).

Practice

  1. State the unit of force.
  2. What is the approximate gravitational force acting on a 100g object, in N?
  3. State all three elements of force.

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