Physics - Term 1 - Week 10

Newton's First Law, also known as the law of inertia, 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 means that if no force is applied, the state of motion of an object will not change. For example, a book lying on a table will not move unless someone pushes it.

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 explains how the velocity of an object changes when it is subjected to an external force. For instance, pushing a shopping cart will accelerate it depending on how hard you push (the force) and how heavy the cart is (the 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; 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. A common example is when you jump off a small boat; as you push down on the boat to jump up, the boat moves backward.

Consider a car with a mass of 1,000 kg that accelerates at 2 m/s². To find the net force acting on the car, we use the formula F = ma. Substituting the values, we get F = 1,000 kg * 2 m/s² = 2,000 N. This means a net force of 2,000 Newtons is required to accelerate the car at that rate.

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 and identify examples of Newton's laws in action. For instance, they can observe a soccer ball being kicked (Newton's Second Law) or a rocket launching into space (Newton's Third Law). Each pair will present their examples to the class, explaining which law is illustrated and how.

Students will complete a worksheet that includes problems related to Newton's laws. For example, they might be asked to calculate the force needed to accelerate a 5 kg object at 3 m/s² or to describe the action-reaction forces involved when a person jumps off a diving board. This will reinforce their understanding and application of the concepts.

• The relationship between force, mass, and acceleration
• The tendency of objects to resist changes in their state of motion
• The action-reaction forces between two objects
• The acceleration of an object due to gravity

Answer: The tendency of objects to resist changes in their state of motion

Newton's First Law, or the law of inertia, states that an object will maintain its 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 mass, and a is acceleration.

• A car accelerating down a hill
• A person pushing against a wall
• A ball rolling on the ground
• A book resting on a table

Answer: A person pushing against a wall

When a person pushes against a wall, the wall pushes back with an equal and opposite force, illustrating Newton's Third Law.

Answer: It continues to move 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.

Answer: Pushing a shopping cart to accelerate it.

When you push a shopping cart, the force you apply causes it to accelerate, demonstrating the relationship between force, mass, and acceleration.

• 40 N
• 14 N
• 10 N
• 4 N

Answer: 40 N

Using F = ma, we calculate F = 10 kg * 4 m/s² = 40 N.