Grade 8 ↓
Force and Newton's laws of motion
In this explainer, we will dive into the world of forces and Newton's laws of motion. This topic is fundamental in physics as it helps us understand how and why objects move. Newton's laws are three principles that describe the relationship between the motion of an object and the forces acting on it. Let's explore these concepts in detail.
What is force?
Force is the push or pull applied to an object. It is what causes an object to move, stop, or change its direction. Forces can cause objects to speed up, slow down, stay in position, or maintain their motion. The unit of force in the International System of Units (SI) is the newton (N).
Examples of forces:
- A man pushing a shopping cart.
- Gravity is pulling an apple down from the tree.
- The wind is pushing the flying kite.
Newton's first law of motion (law of inertia)
Newton's first law states, "An object at rest stays at rest, and an object in motion continues to move with the same speed and direction unless an unbalanced force is applied." This law is also called the law of inertia. Inertia is the tendency of objects to resist a change in their state of motion.
Visual example:
Imagine a soccer ball lying on the ground. It will not start rolling until a player kicks it. Once it starts rolling, it will continue rolling until friction from the ground slows it down and eventually stops it.
Newton's second law of motion
Newton's second law describes how the velocity of an object changes when an external force is applied to it. This law states, "The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass." In equation form, it is expressed as:
F = m * aWhere F is the applied force, m is the mass of the object, and a is the acceleration produced. This law tells us that the greater the mass of an object, the greater the force required to accelerate it.
Visual example:
Consider pushing a car and a bicycle. The car has a greater mass than the bicycle, so it is much harder to push, even if the same force is applied to both.
Newton's third law of motion
Newton's third law is often stated this way "For every action, there is an equal and opposite reaction." This means that forces always come in pairs. If you apply a force to an object, that object will exert an equal force on you in the opposite direction.
Visual example:
When you jump into the water from a small boat, you push the boat backward as you move forward. You may notice that the boat moves in the opposite direction of your jump.
Gravity
Gravity is a force that pulls objects toward one another. It gives physical objects weight, and it causes objects to fall toward Earth. The acceleration due to gravity on Earth is about 9.8 m/s².
Example:
If you drop a ball, gravity pulls it toward the ground. However, the ball also exerts a gravitational force on the Earth, even though we cannot see the Earth move.
Friction
Friction is the force that opposes the motion of an object. It occurs when two surfaces come into contact. Friction is important because it allows us to walk without slipping and vehicles to move on roads without slipping.
Example:
Try sliding a book on a rough and a smooth surface. You will notice that more force is required to slide the book on a rough surface because of increased friction.
Balanced and unbalanced forces
Balanced forces are forces that are equal in size but opposite in direction. They act on the same object but do not cause any change in the motion of the object.
Unbalanced forces are not equal and are opposite. These forces cause a change in the motion of the object.
Visual example:
Consider the game of tug of war. When both teams pull with equal force, the rope doesn't move. This is an example of balanced forces. However, if one team pulls harder than the other, the rope will slide toward the stronger team, which illustrates unbalanced forces.
Conclusion
Understanding forces and motion is essential to explaining how objects in our world interact. Newton's laws of motion provide a framework for analyzing these interactions. By considering the forces acting on an object, we can predict how it will move. From gravity to friction, these forces combine to affect everything from a small ball rolling down a hill to planets orbiting the Sun. All of these phenomena can be understood through the lens of Newton's laws.
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