BeginnerTopic 2 of 106Engineering Mechanics
Newton's laws
Inertia, F=ma and action-reaction are the foundation of classical mechanics.
In depth
First law: a body keeps its state of rest or uniform motion unless a net force acts. Second law: ΣF=ma. Third law: forces between two bodies are equal and opposite. They apply in inertial frames and underpin all of classical mechanics.
Key points
- Inertia is resistance to acceleration
- Action and reaction act on different bodies
- Rotational form ΣM=Iα
ExampleA rocket accelerates because exhaust is pushed backwards, pushing the rocket forward.
What is Newton's laws?
Inertia, F=ma and action-reaction are the foundation of classical mechanics.
Why is it important to understand newton's laws?
These three laws let you predict motion from forces, and nearly every mechanics calculation applies at least one of them.
Why do passengers lurch forward when a car brakes?
Their bodies keep moving at the old speed because of inertia, which is Newton's first law. The seat belt supplies the force that changes their motion.
Does action-reaction mean forces always cancel?
No. The two forces act on different bodies, so they do not cancel when computing the motion of one body.
How is Newton's laws used in practice?
Typical applications include predicting how fast a crate accelerates when pulled by a forklift, explaining why a seat belt is needed in a sudden stop and sizing a motor to accelerate a conveyor load.
What should I learn before Newton's laws?
Study "Force" first (topic 1 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
What are the key points of Newton's laws?
Inertia is resistance to acceleration. Action and reaction act on different bodies. Rotational form ΣM=Iα.
Can you give an example of Newton's laws?
A rocket accelerates because exhaust is pushed backwards, pushing the rocket forward.
What comes after Newton's laws?
The next topic is "Mass vs weight", which builds directly on this one.
How difficult is Newton's laws?
It is classed as Beginner in Engineering Mechanics (topic 2 of 106). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.