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Chapter 4: Problem 4

Does a body necessarily move in the direction of the net force acting on it?

Short Answer

Expert verified
No, a body does not necessarily move in the direction of the net force acting on it. The net force changes the body鈥檚 velocity鈥攁nd hence its direction of motion鈥攂ut it does not instantly make the body move in the direction of the force. The body's motion direction will be a compromise between itsinitial direction of motion before the force acted and the force's direction. This is particularly noticeable when the body already had significant velocity in a different direction before the force started acting. In which case, the body would continue to move in a direction which is the vector sum of the original direction and the direction of the force.

Step by step solution

01

Understanding Motion

Understand that a body moves due to the influence of the forces acting on it. However, its motion is not solely dictated by the current forces exerted on it but also depends on its initial velocity. In a vacuum, without friction or air resistance, a body would keep moving at a constant velocity if no other forces acted on it. If a force is exerted, it modifies this state of motion, but not necessarily in the direction of the force.
02

Analyzing The Role of Force

Consider that a force acting on a body changes its velocity by causing an acceleration. This acceleration occurs in the direction of the force. A body could thus continue to move in a direction different than the net force if it already had a considerable velocity in some direction before the force started acting.
03

Effect of Net Force

Understand that the net force only changes the direction of the object's velocity vector towards the force direction. It doesn't instantly shift the object's motion path towards the force direction. If the object was in motion, part of its velocity vector would remain in the original direction even after acceleration starts. The final motion direction will be a resulting vector depending on the original velocity before the net force acted (also known as inertia) and the acceleration due to the force.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Force and Motion
The relationship between force and motion is a fundamental aspect of physics and often the starting point in learning about dynamics. Motion occurs when an object changes its position over time, and force plays a crucial role in this change. According to Newton's Laws of Motion, a force is what causes a change in an object's state of motion, meaning it can cause an object to start moving, stop, or change direction.

  • A force can accelerate an object, decelerate it, or change its direction.
  • Motion is the result of various forces acting on an object, including gravity, friction, and applied force.
While forces influence motion, the direction of the motion is not necessarily aligned with the force applied. This is because motion also depends on the object's initial velocity, which carries a history of past influences.
Velocity
Velocity is a vector quantity, meaning it has both magnitude and direction. It's different from speed, which only measures how fast an object is moving. When we talk about velocity, we also need to discuss direction, which is crucial in understanding how forces affect motion.

  • Initial velocity greatly determines how an object will continue to move despite a new force being applied.
  • If a new force acts on an object, it will change the velocity by altering either its speed, direction, or both.
When analyzing motion, it's important to consider both the initial velocity and how any new forces will alter this velocity to predict the future state of the object.
Acceleration
Acceleration occurs whenever there is a change in velocity, which can mean speeding up, slowing down, or redirecting. According to Newton's Second Law of Motion, \[ F = ma \]where \( F \) is the force applied, \( m \) is the mass of the object, and \( a \) is the acceleration.

  • Acceleration happens in the direction of the net force acting on the object.
  • It is directly proportional to the force applied and inversely proportional to the object's mass.
Because of this, an object may experience acceleration in a different direction than it is currently moving, depending on its initial velocity.
Net Force
The concept of net force is crucial for understanding how different forces interact to produce motion. Net force is the vector sum of all the individual forces acting on a body. It determines the overall effect of these forces and subsequently the motion of the object.

  • If the net force is zero, the object remains in its current state of motion, moving with constant velocity.
  • If there's a non-zero net force, it will cause an acceleration, altering the object's velocity.
The net force direction can influence the motion, but it may not immediately change the direction of movement if the object has a strong initial velocity in another direction.
Inertia
Inertia is a property of matter that describes an object's resistance to changes in its state of motion or rest. It's how we explain why an object with a certain velocity tends to remain in motion in its initial direction unless acted upon by a net external force.
  • Inertia is directly related to mass: more massive objects have greater inertia.
  • It helps preserve the current state of motion, meaning initial velocity continues unless interrupted by force.
Understanding inertia helps explain why a body can continue moving in a different direction than the net force applied to it, as existing velocity carries forward while the force attempts to alter its path.

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Most popular questions from this chapter

Frogs' tongues dart out to catch insects, with maximum tongue accelerations of about \(250 \mathrm{m} / \mathrm{s}^{2} .\) What force is needed to give a \(500-\mathrm{mg}\) tongue such an acceleration?

A car leaves the road traveling at \(110 \mathrm{km} / \mathrm{h}\) and hits a tree, coming to a stop in 0.14 s. What average force does a seatbelt exert on a \(60-\mathrm{kg}\) passenger during this collision?

A truck crashes into a stalled car. A student trying to explain the physics of this event claims that no forces are involved; the car was just "in the way" so it got hit. Comment.

Although we usually write Newton's second law for one dimensional motion in the form \(F=m a,\) which holds when mass is constant, a more fundamental version is \(F=\frac{d(m v)}{d t} .\) Consider an object whose mass is changing, and use the product rule for derivatives to show that Newton's law then takes the form \(F=m a+v \frac{d m}{d t}\).

An F-16 jet fighter has mass 12 Mg and engine thrust 132 kN. An Airbus \(A-380\) has mass \(560 \mathrm{Mg}\) and total engine thrust \(1.5 \mathrm{MN}\). Could either aircraft climb vertically with no lift from its wings? If so, what vertical acceleration could it achieve?
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