Chapter 2 Newton's First Law of Motion - Inertia
One km in newtons.
10 N of force
kilometer (km)
1000 meters
A cart is pulled to the right with a force of 15 N while being pulled to the left with a force of 20 N. The net force on the cart is?
5 N to the Left
Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 375 N
750 N
Two Pounds in Newtons
9 N
Why do we say that force is a vector quantity?
A force has a magnitude and a direction.
Scalar quantity
A quantity that has only magnitude, not direction, such as mass and volume
A zero net force doesn't mean____
A zero not force doesn't mean that an object must be at rest, only that it's state of motion remains unchanged. It can be at rest or moving in a straight line.
What does it mean to say something is in mechanical equilibrium?
An object in mechanical equilibrium experiences a zero net force.
Newton's First Law, Law of Inertia
An object in motion, or at rest, will tend to stay in motion, or at rest, until it is acted upon by an outside force.
normal
At right angles to, or perpendicular to. A normal force acts at right angles to the surface on which it acts. In optics, a normal defines the line perpendicular to a surface about which angles of light rays are measured.
An airplane flies at constant speed in a horizontal straight path. In other words, the flying plane is in equilibrium. Two horizontal forces act on the plane. One is the thrust of the propeller that pushes it forward, and the other is the force of air resistance that acts in the opposite direction. Which force is greater?
Both forces have the same magnitude. Call the forward force exerted by the propeller positive. Then the air resistance is negative. Since the plane is in dynamic equilibrium, the two forces combine to equal zero? Hence, the plane neither gains nor loses speed.
A bowling ball is in equilibrium when it A) is at rest B) Moves steadily in a straight-line path C) Both D)None
Both. Equilibrium means no change in motion. If at rest, it stays at rest. If in motion, and stays at a steady rate in a straight line, it stays in motion.
normal force
Component of support force perpendicular to a supporting surface. For an object resting on a horizontal surface, it is the upward force that balances the weight of the object.
Newton's first law of motion; the law of inertia
Every object continues in a state of rest or of uniform speed in straight line unless acted on by a nonzero net force.
Equilibrium rule
For any object or system of objects in equilibrium, the sum of the forces acting equals zero. In equation form, ∑F = 0.
What are the units for force?
Force can be expressed in newtons or pounds.
What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa?
Galileo found that a heavier stone does not fall significantly faster than a lighter one.
scale
In music, a succession of notes of frequencies that are in simple ratios to one another.
What did Galileo discover about moving bodies and force in his experiments with inclined planes?
In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.
Force
In the simplest sense, a push or a pull
What type of path does a moving object follow in the absence of a force?
It continues to move in a straight line at a constant speed.
Newton's Laws of Motion
Law 1: Every object continues in a state of rest, or of uniform speed in a straight line, unless acted on by a nonzero net force. Also known as the law of inertia. Law 2: The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object. Law 3: Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.
Would it be correct to say that inertia is the reason a moving object continues in motion when no force acts upon it?
No. We don't know the reason for objects persisting in their motion when no forces act upon them. We refer to the property of material objects to behave in this predictable way as inertia. We don't know why this happens but we call this ignorance inertia.
inertia
Sluggishness or apparent resistance of an object to change its state of motion. Mass is the measure of inertia.
mechanical equilibrium
State of an object or system of objects for which any impressed forces cancel to zero and no acceleration occurs and when no net torque exists. That is, ΣF = 0, and Στ = 0
A force of gravity pulls downward on a book on a table. What force prevents the book from accelerating downward?
Support force
What relationship between the Sun and Earth did Copernicus formulate?
The Earth revolved in a circle about the Sun.
Newton's Second Law of Motion
The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object. The acceleration of an object depends on the mass of the object and the amount of force applied.
According to the parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram?
The diagonal is the resultant, or sum, of two vectors.
If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate?
The frictional force on the crate is 100 N opposite the direction of motion.
What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force?
The net force is 70 pounds to the right.
What is the net force on a bag pulled down by gravity with a force of 18 newtons and pulled upward by a rope with a force of 18 newtons?
The net force is zero newtons.
What is the net force on an object in either static or dynamic equilibrium?
The net force is zero.
Suppose you stand on two bathroom scales with your weight evenly divided between the two scales. What will each scale read? What will happen if you stand with more of your weight on one foot than the other?
The reading on each scale will be half your weight. Then the sum of the scale readings will balance your weight and the net force on you will be zero. If you lean more on one scale than the other, more than half your weight will be read on that scale but less on the other, so they will still add up to your weight. Like the example of the gymnast hanging by the rings, if one scale reads two-thirds your weight, the other scale will read one-third your weight.
Mechanical equilibrium
The state of an object or system of objects for which there are no changes in motion. In accord with Newton's first law, if an object is at rest, the state of rest persists. If an object is moving, its motion continues without change.
The equilibrium rule, applies to____. A) Vector quantities B) Scalar Quantities C) Both D) None
Vector quantities. Vector addition accounts for + and - quantities. So, two vectors in opposite directions can add to zero.
Stand next to a wall that travels at 30 km/s relative to the Sun. With your feet on the ground, you also travel at the same 30 km/s. Do you maintain this speed when your feet leave the ground? What concept supports your answer?
When you jump, you continue to move at 30 km/s due to your inertia.
Newton's Third Law of Motion
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. For every action there is an equal and opposite reaction
When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale?
Your weight is equal in magnitude and opposite in direction to the support force from the scale.
What is the net force on a bathroom scale when a 150-pound person stands on it?
Zero, as evidenced by the scale remaining at rest. The scale reads the support force, which has the same magnitude as weight—not the net force.
Vector quantity
a quantity that has both magnitude and direction, such as force
vector
an arrow drawn to scale used to represent a vector quantity
net force
combination of all the forces that act on an object
The use of inclined planes for Galileo's experiments helped him to______.
discover the property called inertia. Note that the property of inertia is a property of matter.
Resultant
the net result of a combination of two or more vectors
Inertia
the property of things to resit changes in motion
support force
the upward force that balances the weight of an object on a surface
Net Force
the vector sum of forces that act on an object
support force
upward force that balances the weight of an object on a surface. The upward support force must equal the weight of the object it is supporting.
State the equilibrium rule for forces in symbolic notation
ΣF = 0
