Physics - Term 3 - Week 8

A force is a push or pull acting upon an object as a result of its interaction with another object. Forces can cause an object to start moving, stop moving, or change direction. The net force acting on an object is the vector sum of all the individual forces acting on it. Understanding forces is crucial for analyzing motion.

Newton's first law states that an object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity unless acted upon by a net external force. The second law quantifies the relationship between force, mass, and acceleration, expressed by the formula F = ma. The third law states that for every action, there is an equal and opposite reaction, highlighting the interaction between two objects.

Consider a 5 kg object being pushed with a force of 20 N. To find the acceleration, we use the formula F = ma. Rearranging gives us a = F/m. Substituting the values, we have a = 20 N / 5 kg = 4 m/s². Thus, the object accelerates at 4 m/s².

When a swimmer pushes against the wall of a pool, they exert a force on the wall. According to Newton's third law, the wall exerts an equal and opposite force back on the swimmer, propelling them forward. This illustrates how action and reaction forces work in practice.

Let's calculate the net force acting on an object. If a 10 kg object is pulled to the right with a force of 30 N and to the left with a force of 10 N, we first determine the net force. The forces in the same direction add up, while opposing forces subtract. Therefore, the net force is 30 N - 10 N = 20 N to the right.

In pairs, discuss various scenarios and identify the action-reaction pairs. For instance, when a person jumps off a small boat, the action is the person pushing down on the boat, and the reaction is the boat pushing up on the person, causing the boat to move backward.

Solve the following problems independently: 1) A car of mass 800 kg accelerates at 2 m/s². What is the net force acting on the car? 2) If a 15 N force is applied to a 3 kg object, what is its acceleration? 3) Describe an example of Newton's third law in everyday life.

Think of a real-world situation where you can apply Newton's laws. Write a short paragraph explaining how forces are at play in that scenario. For example, consider how seatbelts work in a car during sudden stops, illustrating inertia and the need for forces to change motion.

• Joule
• Newton
• Pascal
• Watt

Answer: Newton

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

• A force acts on it
• It is in motion
• It is heated
• It is pushed

Answer: A force acts on it

Newton's first law states that an object will not change its state of motion unless acted upon by a net external force.

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

Inertia is directly related to mass; the greater the mass of an object, the greater its inertia.

• For every action, there is an equal and opposite reaction
• An object in motion stays in motion
• Force equals mass times acceleration
• Energy cannot be created or destroyed

Answer: Force equals mass times acceleration

Newton's second law quantifies the relationship between force, mass, and acceleration with the formula F = ma.

Answer: When a rocket launches, the engines push down on the ground, and the ground pushes the rocket upward.

This demonstrates action and reaction forces, where the rocket's engines exert a force downward, and the ground exerts an equal force upward.

• 5 m/s²
• 10 m/s²
• 15 m/s²
• 20 m/s²

Answer: 5 m/s²

Using F = ma, rearranging gives a = F/m. Thus, a = 50 N / 10 kg = 5 m/s².

• Frictional force