Senior Secondary Science Programme
Newtonian Mechanics
Teachers' Notes
SubjectPhysics
LevelS4-S6
Duration:15 minutes
Key Points
- Inertia and its relationship to mass.
- Newton’s First Law of motion and uses it to explain situations in which objects are at rest or in uniform motion.
- Effect of force on the speed and/or direction of motion of an object
Content:
Newtonian mechanics is a theory that was established by English scientist Isaac Newton in the 17th century. Through mathematics and experiments, scientists in the 16th century such as Galileo began studying the motion of bodies. Newton followed the works of his predecessors, concluding and further developing their findings to eventually establish the theory of Newtonian mechanics.
1.Newton’s First Law of motion
Newton’s First Law of Motion, also known as “the law of inertia”, states that:
“An object at rest remains at rest and an object in uniform motion remain in uniform motion unless acted upon by an external force.”
The ancient Greek philosopher, Aristotle, said:
“To keep an object in motion, a force needs to be applied continuously on the object.”
Surprisingly this had been allowed to stand for almost 2000 years and yet no one queried it. Maybe this is because Aristotle’s theory seemed to closely reflect our everyday experience.
An object at rest will remain at rest, and an object in motion will remain in its state of uniform motion in a straight line. This property of matter is called “inertia”. The object will eventually stop because the friction between the surface and the object is not zero or negligible.
Various examples were used to illustrate Newton’s first law.
2.Newton’s Second Law of motion
According to Aristotle, “objects can only maintain its motion under continuous application of force. The faster the motion, the greater the force.”
It is clearly a fallacy. It contradicts the law of inertia. According to this law, as long as an object is movingin a straight line atconstantspeed, an external force is not necessary.A force cannot maintain the constant linear motion of an object. A force can change the state of motion of an object.”
In physics, a force is an action which causes the change of motion of an object.
Different examples were used to illustrate the relationship between speed, acceleration and force.
The greater the force applied to an object, the greater its acceleration. This means that force is directly proportional to acceleration. The greater the mass of an object, the larger the amount of force is required to accelerate it. This also means that force is proportional to the mass of the object being accelerated.
Newton’s Second Law can be summarized as follows:
Force is proportional to the product of mass and acceleration. Mathematically, the law can be e expressed as “Force = Mass X Acceleration.”
Suggested Learning Activities
Preparation before viewing the programme
- Teacher may discuss with students how they know about inertia.
- Teacher may discuss with students how they understand the relationship between force and motion of an object.
Activities after viewing the programme
- Student may, under the guidance of teacher, review the physical concepts presented in the programme.
- The teacher may discuss with students how they misinterpret the concept of force before learning the subject.
- Student may perform experiments related to force under the instruction and guidance of teacher.