Physics - Term 2 - Week 9

Newton's First Law states that an object at rest will remain at rest, and an object in motion will continue in motion with the same speed and in the same direction unless acted upon by a net external force. This principle is often referred to as the law of inertia. For example, a book lying on a table will not move unless someone pushes it.

Newton's Second Law quantifies the relationship between force, mass, and acceleration, expressed by the formula F = ma. This means that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. For instance, pushing a car requires more force than pushing a bicycle due to the difference in mass.

Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that forces always occur in pairs. For example, when you jump off a small boat, you push the boat backward as you propel yourself forward.

Consider a 10 kg object being pushed with a force of 50 N. To find the acceleration, we use the formula F = ma. Rearranging gives us a = F/m. Substituting the values, we get a = 50 N / 10 kg = 5 m/s². Thus, the object accelerates at 5 m/s².

If a swimmer pushes the water backwards with a force of 30 N, the water exerts an equal and opposite force of 30 N on the swimmer. This reaction force propels the swimmer forward, demonstrating the principle of action and reaction.

In pairs, discuss the following scenario: A soccer ball is kicked across a field. Identify the forces acting on the ball after it is kicked. Consider air resistance, gravity, and the initial force from the kick. Share your findings with the class.

Using the formula F = ma, calculate the acceleration of a 15 kg cart being pulled with a force of 60 N. Work through the problem together, ensuring each step is understood before moving on.

Complete the following problems independently: 1) A 5 kg object is pushed with a force of 20 N. Calculate its acceleration. 2) Describe a real-life example of Newton's Third Law and explain the action-reaction pair involved.

Write a short paragraph describing how Newton's First Law applies to a passenger in a car that suddenly stops. Discuss the concept of inertia and how it affects the passenger.

• The relationship between force and mass
• The tendency of objects to resist changes in motion
• The action-reaction principle
• The acceleration of an object

Answer: The tendency of objects to resist changes in motion

Newton's First Law, also known as the law of inertia, explains that objects will not change their state of motion unless acted upon by an external force.

• F = ma
• F = mv
• F = m/a
• F = m + a

Answer: F = ma

Newton's Second Law is expressed as F = ma, where F is the net force, m is the mass, and a is the acceleration.

• A ball rolling down a hill
• A rocket launching into space
• A car accelerating on a highway
• A book resting on a table

Answer: A rocket launching into space

When a rocket launches, it expels gas downwards, and in response, the rocket moves upwards, illustrating action and reaction.

Answer: Inertia is the tendency of an object to resist changes in its state of motion.

Inertia is a fundamental concept in physics that describes how objects behave when forces are applied.

Answer: 4 m/s²

Using F = ma, acceleration a = F/m = 80 N / 20 kg = 4 m/s².

• It will stop immediately.
• It will continue moving at a constant velocity.
• It will accelerate.
• It will change direction.

Answer: It will continue moving at a constant velocity.

According to Newton's First Law, an object in motion will remain in motion at a constant velocity unless acted upon by a net external force.