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Newton's Laws - Detailed Help

Assignment NL2: Balanced Forces and the State of Motion

Objectives:

The student should be able to relate the presence of balanced or unbalanced forces to the state of motion of an object.

The student should be able to relate force diagrams and force information to information describing the motion of an object.

Reading:
The Physics Classroom, Newton's Laws Unit, Lesson 1, Part b
The Physics Classroom, Newton's Laws Unit, Lesson 1, Part c

The Physics Classroom, Newton's Laws Unit, Lesson 1, Part d

	A ball is thrown vertically upwards. After the ball is released and is moving upwards towards its peak, it slows down. During this time ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	Many beginning students of Physics believe that an object will always move in the direction of the force which acts upon it. But don't be fooled! Forces are associated with the acceleration direction of an object, not with the direction the object is moving. As such, a forward moving object does not necessarily need a forward force. A forward force would only be needed to speed the object up; if the object is slowing down, a backward force would be required to cause its backward acceleration. And what if the object is moving at a constant speed? Then all the forces acting upon it are balanced.
	Direction of Acceleration: If an object is slowing down, then the direction of its acceleration is opposite the direction which the object is moving. A rightward moving object which is slowing down has a leftward acceleration. And a leftward moving object which is slowing down has a rightward acceleration.
	Why would a rightward (or upward or ...) moving object slow down? What is meant by balanced forces and unbalanced forces?

	When all individual forces acting upon an object are balanced, it is the natural tendency of the object to ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	The phrase in the absence of unbalanced forces means that the individual forces acting upon the object are balanced. Since the forces are balanced, the object's motion is described clearly by Newton's first law of motion (stated above).
	Definition of Accelerate: An object which is said to accelerate is an object which is changing its velocity. The velocity of an object is the speed with a direction. There are three ways to change the velocity: to speed up, to slow down, and to turn or change direction.
	How would an object move in the absence of an unbalanced force? What is meant by balanced forces and unbalanced forces? What does it mean to accelerate?

	Mr. Smith guides a golf ball around the outside rim of the green at the Hole-In-One Putt-Putt Golf Course. When the ball leaves the rim, which path ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	As the golf ball moves around the rim, it pushes upon the rim and the rim pushes back on the ball. This provides an unbalanced force upon the ball. But once the rim ends and the ball is no longer in contact with it, the mutual interaction between wall and ball is over. At that time, the forces acting upon the golf ball are balanced and the motion of the ball is best described by Newton's first law of motion (stated in the Physics Rules section above). The direction the ball is moving when it reaches the edge of the rim is the direction the ball will continue to move. Make O' Isaac proud and get this one right.
	How would an object move in the absence of an unbalanced force? What is meant by the phrase "state of motion"?

	The forces acting upon an object are BALANCED. Therefore, one can be absolutely certain that the object ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	This question requires that you put your thinking cap on. Read (or re-read) Newton's first law above and reflect on what it is saying about objects for which the individual forces are balanced. One of two things can be said about such objects: either they are stationary or they are moving with an unchanging (i.e., constant) speed and direction. One cannot say for certain that the object is at rest or if it is moving with unchanging speed and direction. But one knows positively that whatever state of motion the object is in, it will maintain that state of motion. Now look through the choices given and select those choices which are consistent with an object maintaining its state of motion.
	How would an object move when the forces are balanced? What is meant by balanced forces and unbalanced forces? What is meant by the phrase "state of motion"?

	The forces acting upon an object are NOT BALANCED. Therefore, one can be absolutely certain that the object ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	Newton's first law of motion explains that if the forces acting upon an object are balanced, then the object will maintain its state of motion. To maintain the state of motion is to keep the current speed and direction. But if the forces are not balanced, the object will change its state of motion. In this question, you will have to examine the list of answer choices to determine which choices describe an object which is changing its speed or direction.
	How would an object move when the forces are unbalanced? What is meant by balanced forces and unbalanced forces? What is meant by the phrase "state of motion"?

	If you were in a spaceship and fired a cannonball into frictionless space, the amount of force needed to keep the cannonball in motion would ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	Once in motion an object would continue in motion at constant speed and in the same direction unless acted upon by an unbalanced force. If there is no force to oppose the motion of the cannonball, there is no need to exert a force on the cannonball to keep it in motion. You can kiss this cannonball good-bye.
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	How would an object move in the absence of an unbalanced force? How can one determine the amount of force needed to keep a moving object going at a constant velocity?

	An object moving at a constant velocity MUST ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	Forces when unbalanced cause objects to accelerate. So if an object is moving at a constant velocity, there must NOT be an unbalanced force. If there is no unbalanced force, then the forces acting upon it are balanced.
	What is meant by balanced forces and unbalanced forces? How can one determine the amount of force needed to keep a moving object going at a constant velocity?

	The diagrams below depict the individual forces acting upon an object. Each arrow represents a force and the length of the arrow represents the size of the force. Based on this information, which objects could be moving ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	It is a common misconception to think that a force causes a motion in a given direction. This misconception leads to the further misconception that a motion to the right requires an unbalanced force to the right. But don't be fooled! Forces, when unbalanced, cause accelerations. The direction of the acceleration is the same as the direction of the unbalanced force. Only an acceleration to the right would require an unbalanced force to the right. A motion at constant speed in a given direction is consistent with a balance of forces. Make O' Isaac proud and answer this one right.
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	What does a constant velocity motion indicate about the forces acting upon an object?

	The diagrams below depict the individual forces acting upon an object. Each arrow represents a force and the length of the arrow represents the size of the force. Based on this information, which objects could be moving ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	Forces, when unbalanced, cause objects to accelerate. And the direction of the acceleration is the same as the direction of the force. Forces, when balanced, result in an object either remaining at rest (if at rest) or continuing in motion (if in motion) at a constant velocity. There must be more right force than left force if an object is moving to the right and speeding up. There must be more left force than right force if an object is moving to the right and slowing down. There must be the same amount of right force as left force if the object is moving to the right at a constant speed. If nothing is known about the direction of the acceleration, then nothing can be concluded about the direction of the unbalanced force.
	Click the button below to play an audio file in a separate window.
	What is meant by balanced forces and unbalanced forces? How can one determine the amount of force needed to keep a moving object going at a constant velocity?

	The oil drop diagram below depicts the motion of a rightward-moving object (or a leftward-moving object). Which one of the force diagrams is ...
	Newton's First Law of Motion: An object at rest will tend to stay at rest; an object in motion will tend to stay in motion with the same speed and direction, unless acted upon by an unbalanced force.
	It is a common misconception to think that a force causes a motion in a given direction. This misconception leads to the further misconception that a motion to the right requires an unbalanced force to the right. But don't be fooled! Forces, when unbalanced, cause accelerations. The direction of the acceleration is the same as the direction of the unbalanced force. Only an acceleration to the right would require an unbalanced force to the right. A motion at constant speed in a given direction is consistent with a balance of forces. Make O' Isaac proud and answer this one right.
	Click the button below to play an audio file in a separate window.
	How does one interpret an oil drop diagram (also known as a ticker tape diagram)? What is meant by balanced forces and unbalanced forces? Why would a rightward (or upward or ...) moving object slow down?