Physics - Term 1 - Week 5

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 establishes the relationship between force, mass, and acceleration, expressed by the formula F = ma. This means that the force acting on an object is equal to the mass of that object multiplied by its acceleration. For instance, if you push a shopping cart, the harder you push (greater force), the faster it accelerates, provided the mass remains constant.

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 down on the boat (action), and the boat pushes you up (reaction), causing it to move backward.

Consider a car with a mass of 1000 kg accelerating at 2 m/s². To find the force exerted by the car, we use the formula F = ma. Here, F = 1000 kg * 2 m/s² = 2000 N. This means the car exerts a force of 2000 Newtons to achieve this acceleration.

When a swimmer pushes the water backwards with their hands, they propel themselves forward. If the swimmer exerts a force of 50 N on the water, the water exerts an equal and opposite force of 50 N back on the swimmer, allowing them to move forward.

In pairs, students will discuss various scenarios such as riding a bicycle, playing basketball, or driving a car. They will identify which of Newton's laws apply to each scenario and explain their reasoning. For example, while riding a bicycle, students can discuss how the bicycle remains in motion until they apply brakes (First Law).

Students will complete a worksheet that includes problems requiring them to calculate forces using F = ma, identify real-life examples of each law, and explain the implications of these laws in sports or vehicle safety. For instance, they might calculate the force required to accelerate a 1500 kg car at 3 m/s².

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

Answer: The tendency of objects to resist changes in motion.

Newton's First Law, also known as the law of inertia, describes how objects remain at rest or in uniform motion unless acted upon by an external force.

• F = ma
• F = mv
• F = m/a

Answer: F = ma

Newton's Second Law states that the force acting on an object is equal to the mass of that object multiplied by its acceleration.

• A car accelerating.
• A rocket launching.
• A ball rolling on the ground.

Answer: A rocket launching.

When a rocket launches, it expels gas downwards (action), and the rocket moves upwards (reaction), demonstrating Newton's Third Law.

Answer: The passenger continues to move forward due to inertia.

Inertia causes the passenger to resist the change in motion when the car stops suddenly, which is why seatbelts are important.

Answer: The acceleration decreases.

According to F = ma, if the mass increases and the force is constant, the acceleration must decrease.

• A ball rolling on a flat surface.
• A car accelerating.
• A book resting on a table.

Answer: A car accelerating.

A car accelerating is an example of Newton's Second Law, as it involves a change in motion due to an applied force.