Physics - Term 3 - Week 10

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 relates the force acting on an object to its 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. This law allows us to calculate the effects of forces on 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 crucial in understanding interactions between objects.

Consider a car with a mass of 1,000 kg accelerating at a rate of 2 m/s². To find the force acting on the car, we use the formula F = ma. Here, 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 this rate.

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 interaction illustrates how action and reaction forces work in practice.

Let's work through a problem together. A bicycle with a mass of 15 kg is accelerating at 3 m/s². What is the net force acting on the bicycle? Using F = ma, we calculate F = 15 kg * 3 m/s² = 45 N. Discuss with your partner how this force would change if the mass of the bicycle increased.

Now it's your turn! Solve the following problems on your own: 1) A 5 kg object is subjected to a force of 20 N. What is its acceleration? 2) If a 10 kg cart is pushed with a force of 50 N, what will be its acceleration? Show your calculations and be prepared to discuss your answers.

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

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

Newton's First Law is all about inertia, which is the resistance of any physical object to any change in its velocity.

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

Answer: F = ma

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

• 10 N
• 7 N
• 12 N
• 15 N

Answer: 10 N

Using F = ma, we calculate F = 2 kg * 5 m/s² = 10 N.

Answer: For every action, there is an equal and opposite reaction.

This law indicates that forces always occur in pairs; one force is the action and the other is the reaction.

• A car accelerating down a hill.
• A rocket launching into space.
• A ball rolling on the ground.
• A person pushing against a wall.

Answer: A person pushing against a wall.

When a person pushes against a wall, the wall pushes back with an equal force, illustrating action and reaction.

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

Inertia is a key concept in Newton's First Law, highlighting how objects behave when forces are applied.