Chapter 1: An Introduction to Statics

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1.3:

Leis do Movimento de Newton

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Mechanical Engineering

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JoVE Core Mechanical Engineering

Newton’s Law of Motion

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1.2: Basic Concept

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1.4: Newton’s Law of Gravitational Attraction

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An object's motion or stillness can be explained using Newton's laws of motion. The first law states that an object at rest stays at rest and an object in motion stays in motion at a constant speed and direction unless acted upon by an unbalanced force. A football stays at rest until it is kicked by a player and stays in motion until an external force is applied to bring it back to rest. The second law of motion states that when an unbalanced force acts upon a body, it experiences an acceleration that has a magnitude directly proportional to the force and has the same direction as the force. Consider a man with a cart. When he applies force to the cart, the cart moves in the direction of the applied force. The third law states that for every action, there is an equal and opposite reaction. When a moving car hits a stationary truck, it exerts an equal and opposite force on the car.

1.3:

Leis do Movimento de Newton

When we observe objects around us, one question that comes to mind is why they move or stay still. The answer to this question can be explained using Newton's laws of motion. These laws describe the fundamental principles of motion and the effects of forces on objects.

The first law of motion, also known as the law of inertia, states that an object at rest will stay at rest, and an object in motion will continue to move at a constant speed and direction unless acted upon by an external force. For example, when a sliding box slows down on its own, the net external force on the box is the friction force that acts against the box's motion to slow it down.

Newton's first law considers bodies at rest or in motion at a constant velocity. However, if the velocity of the object changes, then the accelerated motion is addressed by Newton's second law. The second law of motion describes how an object responds to an unbalanced force acting upon it. The law states that the acceleration of an object is directly proportional to the force exerted on it and inversely proportional to its mass. For example, when a person hits a ball, it moves with an acceleration directly proportional to the force applied to it.

The third law of motion, also known as the law of action and reaction, states that for every action, there is an equal and opposite reaction. For example, if a person stands on roller skates and throws a ball forward, then it is likely that the person will start moving backward at a given speed.

Newton's laws of motion have many applications in the real macroscopic world. For example, the laws can be used to design structures and machines that can withstand external forces. The trajectory of celestial objects or rockets can also be calculated using Newton's laws of motion.

In conclusion, Newton's laws of motion provide a foundation for understanding the relationship between forces and motion. These laws are fundamental to many fields of science and have practical applications that impact our daily lives. Whether we're watching a football game or launching a spacecraft, we rely on these laws to explain the motion of objects and the effects of forces on them.

Suggested Reading

Hibbeler, R.C. (2016). Engineering Mechanics ‒ Statics and Dynamics. Hoboken, New Jersey: Pearson Prentice Hall. Pp 4 ‒ 5.
Beer, F.P.; Johnston, E.R.; Mazurek, D.F; Cromwell, P.J. and Self, B.P. (2019). Vector Mechanics for Engineers ‒ Statics and Dynamics. New York: McGraw-Hill. Pp – 3.
Meriam, J.L.; Kraige, L.G., and Bolton, J.N. (2020). Engineering Mechanics ‒ Statics. Hoboken, New Jersey: John Wiley. Pp – 2.