CHAPTER 3: FORCES. SECTION 1 (PART 1) - Introduction to Forces and Newton’s 2 nd Law Of Motion.
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Transcript of CHAPTER 3: FORCES. SECTION 1 (PART 1) - Introduction to Forces and Newton’s 2 nd Law Of Motion.
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CHAPTER 3: FORCES
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SECTION 1 (PART 1) - Introduction to Forces and
Newton’s 2nd Law Of Motion
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WARM-UP: How did we
previously define the term “force”?
Describe the relationship between forces and motion.
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LEARNING GOALS:Distinguish between the different types of forces.
Define and apply Newton’s 2nd Law of Motion.
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TYPES OF FORCESThere are actually many types of forces including:
1. Applied force
2. Frictional force
3. Gravitational force
4. Normal force
5. Thrust
6. Drag
7. Lift
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APPLIED FORCE Objects are often
touching
A push or a pull on anything
Contact force Example: A person
picking up a box applies a force the the box in order to pick it up.
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FRICTIONAL FORCE Works opposite of an object’s
motion
Takes away energy
Works to slow down or stop objects
Contact force Example: As cart moves along the
road, friction slows the cart down.
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GRAVITATIONAL FORCE Pulls toward the center of the
earth
Non-contact force
Relatively constant on Earth, regardless of location and size of the object
Example: A stone thrown in the air will be pulled back down to the Earth’s surface.
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NORMAL FORCE Opposes gravity
Contact force
Usually upward
Does not cause acceleration
Usually equal and opposite to the applied force
Example: The book sitting on the table has a normal force holding it up.
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THRUST Rockets, planes, boats Something pushes
backwards causing forward motion
Gas, water, air pushed by engines, propellers, or explosions Example: An airplanes thrust
is provided by its engines.
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DRAG Air resistance Type of friction Opposes the motion of an
object Moving through water can
also cause drag on a boat Example: As the airplane
moves through the air the force of drag pushes back on the airplane.
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LIFT Opposes gravity Lift is usually “upward” Causes airplanes, hot air
balloons to go up but not forward Example: The force of lift
pushes the airplane up and thrust pushes it forward.
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NEWTON’S LAWS OF MOTION Sir Isaac Newton
published his three laws of motion in his book Principia in 1687.
Laws describe the effects of forces on the motion of objects.
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NEWTON’S 1ST LAW OF MOTION (aka INERTIA) An object moving at a constant
velocity keeps moving at that velocity unless an unbalanced net force acts upon it.
An object at rest will stay at rest unless an unbalanced force acts upon it.
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NEWTON’S 2ND LAW OF MOTION Newton’s 2nd Law of Motion: the
acceleration of an object is in the same direction as the net force on the object.
Also states that acceleration is equal to the net force divided by mass
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NEWTON’S 2ND LAW OF MOTION An object will have greater acceleration
if a greater force is applied to it.
Tossingvs.
Throwing
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NEWTON’S 2ND LAW OF MOTION The mass of the object also affects
acceleration. A softball’s mass is about 0.20 kg while a baseball’s mass is
about 0.14 kg. If you throw both with the same force, the baseball has greater acceleration because it has less mass.
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USING NEWTON’S 2ND LAW Force = mass / acceleration F = force in Newtons (N) m = mass in kilograms (kg) a = acceleration in meters per
second squared (m/s2)
F = ma
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FORMULA SHEET
F = mam = F/aa = F/m
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EXAMPLE PROBLEM #1 Engineers must determine the net force needed
for a rocket to achieve an acceleration of 70 m/s2. If the mass of the rocket is 45,000 kg, how much net force must the rocket develop?
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EXAMPLE PROBLEM #2 What is the mass of a truck if it produces a
force of 14,000 N while accelerating at a rate of 5 m/s2 ?
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EXAMPLE PROBLEM #3 If the mass of a helicopter is 4,500 kg, and
the net force on it is 18,000 N, what is the helicopter’s acceleration?