9TH GRADE · NEWTON'S LAWS
Gravity, elasticity, weight and friction
Universal gravity, Hooke's law, overload and weightlessness.
The entire theory of the lesson is collected here; you can read it without an account. In interactive mode, the same theory appears as cards, followed by questions. with checking the answer and task, and progress is saved.
Basic Concepts
Universal gravity
Any two bodies attract with a force depending on their masses and the distance between them.
For spheres, the distance is taken between centers; acceleration g depends on the mass and radius of the celestial body, so it is different on other planets.
Weight, overload and weightlessness
The weight depends on the acceleration of the support: when accelerating upward, it increases, and during free fall it becomes zero.
Weightlessness does not mean the disappearance of gravity; the body and the support simply fall with the same acceleration.
Elasticity and friction
Elasticity is associated with deformation and tends to restore shape, while friction prevents the relative movement of surfaces.
In the experiment, stiffness is found from the slope of the graph of force versus elongation while Hooke's law is satisfied.
Physical quantities
Gravity
The force of attraction of a body by a planet near the surface.
Unit: newton ·
Weight
The force exerted by a body on a support or suspension.
Unit: newton ·
Elastic force
The force arising during elastic deformation.
Unit: newton ·
Elongation
Change in the length of an elastic body.
Unit: meter ·
Hardness
Coefficient of proportionality between elastic force and elongation.
Unit: newton per meter ·
Gravitational constant
Coefficient of the law of universal gravitation.
Unit: newton square meter per square kilogram ·
Lesson formulas
Law of Gravity
The force of gravity is proportional to the product of masses and inversely proportional to the square of the distance.
Gravity
The force of gravity at the surface is equal to the product of mass and the acceleration of gravity.
Hooke's law
The modulus of elastic force is equal to the product of stiffness and elongation.
Condition: The deformation is elastic and quite small.
Weight at vertical acceleration
When the support accelerates upward, the weight is equal to mass times the sum of g and acceleration.
Related formulas
The same formulas in the reference, with symbols and units.
Tasks on the topic
Statements, answer options and the walkthrough.