Physics 12 Quarter 1 Module 4 | Lecture notes Physics

GENERAL PHYSICS 1: MODULE 5

The following are the lessons contained in this module:

1. NEWTON’S LAWS OF MOTION AND ITS APPLICATION

2. NEWTON’S LAW OF UNIVERSAL GRAVITATION

3. APPLYING NEWTON’S LAWS OF MOTION

At the end of this module, you are expected to:

Apply Newton’s 1st law to obtain quantitative and qualitative conclusions about the contact and

noncontact forces acting on a body in equilibrium (STEM_GP12N-Ie-33)

Apply Newton’s 2nd law and kinematics to obtain quantitative and qualitative conclusions

about the velocity and acceleration of one or more bodies, and the contact and noncontact

forces acting on one or more bodies (STEM_GP12N-Ie-36)

Identify action-reaction pairs (STEM_GP12N-Id-31)

Solve problems using Newton’s Laws of motion in contexts such as, but not limited to, ropes and

pulleys, the design of mobile sculptures, transport of loads on conveyor belts, force needed to

move stalled vehicles, determination of safe driving speeds on banked curved roads

(STEM_GP12N-Ie-38)

Lesson 6

NEWTON’S LAWS OF MOTION AND ITS APPLICATION

A body is said to be in motion (or moving) when it is position changes continuously with respect

to a stationary object taken as reference point. The study of motion is kinematics, but kinematics only

describes the way objects move—their velocity and their acceleration. Dynamics considers the forces

that affect the motion of moving objects and systems. Newton’s laws of motion are the foundation of

dynamics. These laws provide an example of the breadth and simplicity of principles under which

nature functions. They are also universal laws in that they apply to similar situations on Earth as well as

in space. Many things can be explained by the use of actual observations and some are

explained by simple common sense.

The laws were developed by Sir Isaac Newton in the late 1600s. Isaac Newton’s

(1642–1727) laws of motion were just one part of the monumental work that has made

him legendary. The development of Newton’s laws marks the transition from the

Renaissance into the modern era. This transition was characterized by a revolutionary

change in the way people thought about the physical universe. Newton made use of the

work of his predecessors, which enabled him to develop laws of motion, discover the

law of gravity, invent calculus, and make great contributions to the theories of light

and color. It is amazing that many of these developments were made with Newton working

alone, without the benefit of the usual interactions that take place among scientists today.

NEWTON’S FIRST LAW OF MOTION (Law of Inertia) states that an object’s motion will not change

unless an unbalanced force acts on the object. If the object is at rest, it will stay at rest. If the object is

in motion, it will stay in motion and its velocity will remain the same. In other words, neither the

direction nor the speed of the object will change as long as the net force acting on it is zero.

INERTIA is the tendency of an object to resist changes in its velocity: whether in motion or

motionless. Objects wants to stay in rest or motion unless an outside force causes a change.

oFor example, if you roll a ball, it will continue rolling unless friction or something else

stops it by force.

Let’s look at another situation. Refer to for this example. Why do we

wear seat belts? Obviously, they’re there to protect us from injury in

case of a car accident. If a car is traveling at 80 km/h, the driver is also

traveling at 80 km/h. When the car suddenly stops, an external force is

applied to the car that causes it to slow down. But there is no force

acting on the driver, so the driver continues to travel at 80 km/h. The

seat belt is there to counteract this and act as that external force to

slow the driver down along with the car, preventing them from being

harmed.

Think about what happens when you are riding in a car that stops suddenly. Your body moves

forward on the seat. Why? The brakes stop the car but not your body, so your body keeps moving

forward because of inertia. That’s why it’s important to always wear a seat belt. The car keeps

changing direction, but the riders keep moving in the same direction as before. They slide to the

opposite side of the car as a result.

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The following are the lessons contained in this module:

**1. NEWTON’S LAWS OF MOTION AND ITS APPLICATION

NEWTON’S LAW OF UNIVERSAL GRAVITATION
APPLYING NEWTON’S LAWS OF MOTION** At the end of this module, you are expected to:  Apply Newton’s 1st law to obtain quantitative and qualitative conclusions about the contact and noncontact forces acting on a body in equilibrium (STEM_GP12N-Ie-33)  Apply Newton’s 2nd law and kinematics to obtain quantitative and qualitative conclusions about the velocity and acceleration of one or more bodies, and the contact and noncontact forces acting on one or more bodies (STEM_GP12N-Ie-36)  Identify action-reaction pairs (STEM_GP12N-Id-31)  Solve problems using Newton’s Laws of motion in contexts such as, but not limited to, ropes and pulleys, the design of mobile sculptures, transport of loads on conveyor belts, force needed to move stalled vehicles, determination of safe driving speeds on banked curved roads (STEM_GP12N-Ie-38) Lesson 6

NEWTON’S LAWS OF MOTION AND ITS APPLICATION

A body is said to be in motion (or moving) when it is position changes continuously with respect to a stationary object taken as reference point. The study of motion is kinematics, but kinematics only describes the way objects move—their velocity and their acceleration. Dynamics considers the forces that affect the motion of moving objects and systems. Newton’s laws of motion are the foundation of dynamics. These laws provide an example of the breadth and simplicity of principles under which nature functions. They are also universal laws in that they apply to similar situations on Earth as well as in space. Many things can be explained by the use of actual observations and some are explained by simple common sense. The laws were developed by Sir Isaac Newton in the late 1600s. Isaac Newton’s (1642–1727) laws of motion were just one part of the monumental work that has made him legendary. The development of Newton’s laws marks the transition from the Renaissance into the modern era. This transition was characterized by a revolutionary change in the way people thought about the physical universe. Newton made use of the work of his predecessors, which enabled him to develop laws of motion, discover the law of gravity, invent calculus, and make great contributions to the theories of light and color. It is amazing that many of these developments were made with Newton working alone, without the benefit of the usual interactions that take place among scientists today. NEWTON’S FIRST LAW OF MOTION (Law of Inertia) states that an object’s motion will not change unless an unbalanced force acts on the object. If the object is at rest, it will stay at rest. If the object is in motion, it will stay in motion and its velocity will remain the same. In other words, neither the direction nor the speed of the object will change as long as the net force acting on it is zero.  INERTIA is the tendency of an object to resist changes in its velocity: whether in motion or motionless. Objects wants to stay in rest or motion unless an outside force causes a change. o For example, if you roll a ball, it will continue rolling unless friction or something else stops it by force. Let’s look at another situation. Refer to for this example. Why do we wear seat belts? Obviously, they’re there to protect us from injury in case of a car accident. If a car is traveling at 80 km/h, the driver is also traveling at 80 km/h. When the car suddenly stops, an external force is applied to the car that causes it to slow down. But there is no force acting on the driver, so the driver continues to travel at 80 km/h. The seat belt is there to counteract this and act as that external force to slow the driver down along with the car, preventing them from being harmed. Think about what happens when you are riding in a car that stops suddenly. Your body moves forward on the seat. Why? The brakes stop the car but not your body, so your body keeps moving forward because of inertia. That’s why it’s important to always wear a seat belt. The car keeps changing direction, but the riders keep moving in the same direction as before. They slide to the opposite side of the car as a result.

Why then, do we observe everyday objects in motion slowing down and becoming motionless seemingly without an outside force? It’s a force we sometimes cannot see – FRICTION. Friction is a force between two surfaces that are sliding, or trying to slide, across each other. For example, when you try to push a book along the floor, friction makes this difficult. Friction always works in the direction opposite to the direction in which the object is moving, or trying to move.

Friction has both negative and positive aspects. Friction reduces the efficiency of machines. On the other hand, we couldn't walk or run without friction.
There are two types of friction: kinetic friction and static friction. Kinetic friction is the friction encountered when surfaces slide against one another.
The magnitude of the force of kinetic friction depends on the normal force.
As the figure below indicates, the force of kinetic friction is proportional to the normal force: Doubling the normal force doubles the force of kinetic friction.
The constant μ k in the equation is referred to as the coefficient of kinetic friction. The larger the coefficient of friction, the greater the force of friction. Static friction is the force that opposes the sliding of one nonmoving surface past another.
Like kinetic friction, static friction is due to microscopic surface irregularities.
As the figure shows, the force of static friction can have values ranging from zero to some well-defined maximum.
A stationary object begins to move when the applied force equals the maximum force of static friction. Once an object is moving, kinetic friction comes into play.
The maximum force that static friction can exert is given by the following expression:  In this equation, μ s is the coefficient of static friction.  In general, μ s is greater than μ k. This means that the force of static friction is usually greater than the force of kinetic friction. Friction plays an important role in driving safety. When a car is moving with its tires rolling freely, the friction between the tires and the road is static friction. Why is this so? Even though the car and tires are moving forward, at any instant the bottom of the tire is at rest with respect to the ground. In the absence of a force of friction, a moving body would continue its motion with the same speed and direction - forever! #MayForever 😊

There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces. Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift. The reaction of a rocket is an application of the third law of motion. Various fuels are burned in the engine, producing hot gases. The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction. PRACTICE EXERCISE:

Find the force needed to accelerate a 100 kg mass by 20 m/s². Ans: 2000 N
1. An aircraft has a mass of 500 000 kg. The total force from its jet engines is 800 000 N. What is its acceleration? Ans: 1.6 m/s²
A net force of 16 N causes a mass to accelerate at a rate of 5 m/s 2. Determine the mass. Ans: 3. kg
What is the force on a 1000 kg elevator that is in free fall? Ans: 9800 kg- m/s^2 or 9800 N

Lesson 7

NEWTON’S LAW OF UNIVERSAL GRAVITATION

If the planets are orbiting the sun, what force is keeping them in orbit? What force keeps the moon in its orbit? NEWTON’S LAW OF UNIVERSAL GRAVITATION. Any two objects attract each other with a gravitational force, proportional to the product of their masses and inversely proportional to the square of the distance between them. The force acts in the direction of the line connecting the centers of the masses. Henry Cavendish’s experiment determined the proportionality constant G in 1798. The Value of G:

G= 6.67 x 10

N m

/ kg

2 Change of Gravitational Force with Distance Law of universal gravitation is known as an inverse square law. PRACTICE EXERCISE: Two spheres A and B of mass 35kg and 26 kg, respectively are 60m apart.

What force does one exert on the other? ANS: 1.69 x 10-11^ N
If the mass of sphere A is tripled and the distance between the spheres is quadrupled how does the force change? ANS: FCHANGE = FFINAL – FINITIAL => FCHANGE = 3.16 x 10-12^ N - 1.69 x 10-11^ N= - 1.37 x 10-11^ N

Lesson 8

APPLYING NEWTON’S LAWS OF MOTION

FORCE - push or pull

 is an interaction between two bodies or between a body and its environment

 a vector quantity, with magnitude and direction

The force, F , which acts at an angle Ɵ from the x-axis, may be replaced by its rectangular component vectors Fx and Fy.

SAMPLE PROBLEM:

The finalist for the boxing tournaments are fighting over a champion's belt. The figure (a) shows the horizontal force each wrestler applies to the belt, as viewed from above. The forces have magnitudes F1= 250 N, F2= 50 N, and F3= 120 N. Find the x- and y-components of the net force on the belt, and its magnitude.

Physics 12 Quarter 1 Module 4, Lecture notes of Physics

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NEWTON’S LAWS OF MOTION AND ITS APPLICATION

Lesson 7

NEWTON’S LAW OF UNIVERSAL GRAVITATION

G= 6.67 x 10

N m

/ kg

Lesson 8

FORCE - push or pull

 is an interaction between two bodies or between a body and its environment

 a vector quantity, with magnitude and direction

SAMPLE PROBLEM:

1. A waitress shoves a ketchup bottle with mass 0.45 kg to her right along a smooth, level

lunch counter. The bottle leaves her hand moving at 2.8 m/s, then slows down as it

slides because of a constant horizontal friction force exerted on it by the countertop. It

slides for 1.0 m before coming to rest. What are the magnitude and direction of the

friction force acting on the bottle?

2. A 2.49 X 10^4 N Nissan Navarra traveling in the -direction makes an emergency stop; the

x-component of the net force acting on it is -1.83 x 10^4 N. What is its acceleration?