Physics - Term 1 - Week 3

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 law emphasizes the concept of inertia, which is the tendency of an object to resist changes in its state of motion.

Newton's Second Law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This can be expressed with the formula F = ma, where F is the net force, m is the mass, and a is the acceleration. This law helps us understand how forces affect the motion of objects.

Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that forces always occur in pairs; when one object exerts a force on another, the second object exerts a force of equal magnitude but in the opposite direction on the first object. This principle is evident in various interactions, such as walking or swimming.

Consider a soccer ball lying on the ground. It will not move unless a player kicks it, demonstrating that an object at rest stays at rest until acted upon by an external force. If the ball is rolling on a smooth surface, it will continue to roll indefinitely unless friction or another force slows it down.

If a car with a mass of 1,000 kg accelerates at 2 m/s², we can calculate the net force acting on it using F = ma. Here, F = 1,000 kg * 2 m/s² = 2,000 N. This shows how the mass and acceleration relate to the force applied.

When a swimmer pushes against the water with their hands, they exert a force on the water. According to Newton's Third Law, the water exerts an equal and opposite force back on the swimmer, propelling them forward. This interaction illustrates how action and reaction forces work.

In pairs, students will discuss and identify examples of each of Newton's laws in everyday situations. For instance, they can consider how a book on a table illustrates the first law, or how a car accelerates when the driver presses the gas pedal relates to the second law. Each pair will share their examples with the class.

Students will complete a worksheet that includes problems requiring them to apply Newton's laws. For example, they might calculate the force needed to accelerate a 5 kg object at 3 m/s² or describe the forces acting on a skateboarder pushing off the ground. This will reinforce their understanding and application of the concepts.

• 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 emphasizes inertia, which is the resistance of any physical object to any change in its velocity.

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

Answer: F = ma

Newton's Second Law is defined by the equation F = ma, indicating the relationship between force, mass, and acceleration.

• The wall moves towards you
• You feel no force
• The wall pushes back with an equal force
• You fall over

Answer: The wall pushes back with an equal force

Newton's Third Law states that for every action, there is an equal and opposite reaction, meaning the wall exerts an equal force back on you.

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: A car accelerating when the driver presses the gas pedal.

This example illustrates how the force applied results in acceleration, demonstrating the relationship defined by Newton's Second Law.

• Kilogram
• Newton
• Meter
• Joule

Answer: Newton

The SI unit of force is the Newton, which is defined as the force required to accelerate a one-kilogram mass by one meter per second squared.