Which statement is true about forces
Answers
The forces are defined by both strength and direction is a true statement.
Answer:
Force
A force is an interaction between objects that tends to produce acceleration of the objects.
A force is a vector, with both a magnitude and a direction.
The MKS unit of force is the newton (N). 1 N = 1 kg m / s2.
Acceleration occurs when there is a net force on an object; no acceleration occurs when the net force (the sum of all the forces) is zero. An acceleration produces a change in velocity (magnitude and/or direction), so an unbalanced force will change the velocity of an object.
Isaac Newton (1642-1727) studied forces and noticed three things in particular about them. These are important enough that we call them Newton's laws of motion.
Newton's First Law
Aristotle (384-322 BC) thought that objects were naturally at rest.
Galileo (1564-1642) realized that the Greeks weren't accounting for forces such as friction.
Newton summarized Galileo's thoughts in the following statement:
Newton's first law: an object at rest tends to remain at rest, and an object in motion tends to remain in motion with a constant velocity (constant speed and direction of motion), unless it is acted on by a nonzero net force.
The net force is the sum of all the forces acting on an object.
The tendency of an object to maintain its state of motion is known as inertia. Mass is a good measure of inertia; light objects are easy to move, but heavy objects are much harder to move, and it is much harder to change their motion once they start moving.
Do Newton's laws apply all the time? As long as we're in a stationary reference frame, or even moving at constant velocity, Newton's law are valid. Such reference frames are called inertial reference frames.
Newton's Laws are not enough to account for motion observed from non-inertial (accelerating) reference frames.
Newton's Second Law
What is the acceleration produced by applying a force to an object? Newton's second law states that the acceleration of an object is proportional to the net force and inversely proportional to the mass of the object.
Newton's Second Law: ΣF = m a
Newton's Third Law
A force is an interaction between objects, and forces exist in equal-and-opposite pairs. These statements are summarized by:
Newton's third law: when one object exerts a force on a second object, the second object exerts an equal-and-opposite force on the first object.
"equal-and-opposite" is short for "equal in magnitude but opposite in direction".
Although the forces between two objects are equal-and-opposite, the effect of the forces may or may not be similar - it depends on the relative masses of the objects.
If we drop a 100 g (0.1 kg) ball, it experiences a downward acceleration of 9.8 m/s2, and a force of about 1 N, because it is attracted towards the Earth. The ball exerts an equal-and-opposite force on the Earth, so why doesn't the Earth accelerate upwards towards the ball?
It does, but the mass of the Earth is so large (6.0 x 1024 kg) that the acceleration is much too small (about 1.67 x 10-25 m/s2) for us to notice.
When objects have similar mass, the equal-and-opposite pairs of forces are much easier to see.
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