Physics 2024 Module 2: Dynamics
Module 2: Dynamics
Principal Focus: Students develop their knowledge,understanding and skills relevant to the study of motion.
Students examine energy in its different forms, and how we describe and measure electricity and magnetism and
their interrelated effects.
Physics is a science that is grounded in experimentation. Often when we think about Physics, we think about
great theories such as Newton’s Law of Gravity or Einstein’s Theory of Special Relativity. These are not (and
have never been) the focus of Physics. These theories (and Physics in general) aim to explain the experiments and
observations that we make.
Physics Syllabus
Newton’s Laws
“What are forces, and how do they affect motion?”
A force is generally considered a push or pull that is exerted onto an object. The concept of a force has been
studied for many centuries, but it was not until Sir Isaac Newton developed his 3 laws that the study of forces
took a more quantitative approach. Forces can be categorised based on how they act on other objects:
● Contact Force: The force is transmitted because of physical contact between two objects.
● Non-contact Force (action at a distance): The force is transmitted without any object being in contact.
All non-contact forces are transmitted through fields. We often say that fields mediate these forces.
Fields are simply defined as points in space where a force is felt.
Force is a vector quantity and thus has both magnitude and direction. The S.I. unit for force is Newton (N).
Before we look at each of Newton’s Laws, we should first attempt to understand the concept of mass.
Newton’s First Law
Newton’s First Law is often called the law of inertia.Newton’s first law states that:
“ An object at rest or travelling at a constant velocity will continue to do so, unless it is acted upon by a net force “
What this means is that an object that is stationary will remain stationary unless there is a net force. A net force
can be thought of as an external unbalanced force. The net force is the vector sum of all forces. This also applies
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, Physics 2024 Module 2: Dynamics
to when an object is travelling at a constant velocity. In both cases (stationary and travelling at a constant
velocity) the acceleration is zero.
An unbalanced force can be applied to an object, and when this is done we can cause it to change its motion.
Let’s compare the force required to change the motion of a car, and a coin.
If a car is stationary (i.e. no acceleration) then to move it you would require a large net force. Conversely, a coin
does not require a large net force to make it move. Now, the difference between the two is clearly their mass. In
dynamics we refer to this difference as a difference in inertia. Inertia is the tendency of an object to resist
acceleration.
Inertial Frame of Reference
Recall that a frame of reference is a set of coordinates (an origin and positive directions) that can be used to make
measurements relative to. A frame of reference that is not accelerating is said to be an inertial frame of reference.
Within Newtonian mechanics (also called classical mechanics) all inertial reference frames behave the same. This
means that we treat a frame of reference that is stationary the same as one that is moving at a constant velocity.
An inertial frame of reference is one that is not accelerating
Newton’s Second Law
Newton’s second law is one of the most important laws in all of Physics. It is simply a mathematical statement
that relates the forces acting on an object to its acceleration.
𝐹⃗ = 𝑚𝑎⃗ or Σ𝐹⃗ = 𝑚𝑎⃗
Both forms of the second law can be used. It states that the NET force is equal to the mass of the object(s)
multiplied by their acceleration.
Here we use the concept of the NET force. The net force is simply a vector sum of all forces. As we have
previously seen, we can either use vector addition in 2-dimensions to perform this vector addition or break the
forces up into their components and then add them. The act of breaking up into their components is often
referred to as resolving the forces into their components.
Newton’s Third Law
Newton’s third law is often referred to as the action-reaction law.
Whenever an object A exerts a force on object B, object B will exert a force on object A that is equal in magnitude but
opposite in direction.
12
Module 2: Dynamics
Principal Focus: Students develop their knowledge,understanding and skills relevant to the study of motion.
Students examine energy in its different forms, and how we describe and measure electricity and magnetism and
their interrelated effects.
Physics is a science that is grounded in experimentation. Often when we think about Physics, we think about
great theories such as Newton’s Law of Gravity or Einstein’s Theory of Special Relativity. These are not (and
have never been) the focus of Physics. These theories (and Physics in general) aim to explain the experiments and
observations that we make.
Physics Syllabus
Newton’s Laws
“What are forces, and how do they affect motion?”
A force is generally considered a push or pull that is exerted onto an object. The concept of a force has been
studied for many centuries, but it was not until Sir Isaac Newton developed his 3 laws that the study of forces
took a more quantitative approach. Forces can be categorised based on how they act on other objects:
● Contact Force: The force is transmitted because of physical contact between two objects.
● Non-contact Force (action at a distance): The force is transmitted without any object being in contact.
All non-contact forces are transmitted through fields. We often say that fields mediate these forces.
Fields are simply defined as points in space where a force is felt.
Force is a vector quantity and thus has both magnitude and direction. The S.I. unit for force is Newton (N).
Before we look at each of Newton’s Laws, we should first attempt to understand the concept of mass.
Newton’s First Law
Newton’s First Law is often called the law of inertia.Newton’s first law states that:
“ An object at rest or travelling at a constant velocity will continue to do so, unless it is acted upon by a net force “
What this means is that an object that is stationary will remain stationary unless there is a net force. A net force
can be thought of as an external unbalanced force. The net force is the vector sum of all forces. This also applies
11
, Physics 2024 Module 2: Dynamics
to when an object is travelling at a constant velocity. In both cases (stationary and travelling at a constant
velocity) the acceleration is zero.
An unbalanced force can be applied to an object, and when this is done we can cause it to change its motion.
Let’s compare the force required to change the motion of a car, and a coin.
If a car is stationary (i.e. no acceleration) then to move it you would require a large net force. Conversely, a coin
does not require a large net force to make it move. Now, the difference between the two is clearly their mass. In
dynamics we refer to this difference as a difference in inertia. Inertia is the tendency of an object to resist
acceleration.
Inertial Frame of Reference
Recall that a frame of reference is a set of coordinates (an origin and positive directions) that can be used to make
measurements relative to. A frame of reference that is not accelerating is said to be an inertial frame of reference.
Within Newtonian mechanics (also called classical mechanics) all inertial reference frames behave the same. This
means that we treat a frame of reference that is stationary the same as one that is moving at a constant velocity.
An inertial frame of reference is one that is not accelerating
Newton’s Second Law
Newton’s second law is one of the most important laws in all of Physics. It is simply a mathematical statement
that relates the forces acting on an object to its acceleration.
𝐹⃗ = 𝑚𝑎⃗ or Σ𝐹⃗ = 𝑚𝑎⃗
Both forms of the second law can be used. It states that the NET force is equal to the mass of the object(s)
multiplied by their acceleration.
Here we use the concept of the NET force. The net force is simply a vector sum of all forces. As we have
previously seen, we can either use vector addition in 2-dimensions to perform this vector addition or break the
forces up into their components and then add them. The act of breaking up into their components is often
referred to as resolving the forces into their components.
Newton’s Third Law
Newton’s third law is often referred to as the action-reaction law.
Whenever an object A exerts a force on object B, object B will exert a force on object A that is equal in magnitude but
opposite in direction.
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