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Page 1: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Physical Physical ScienceScience

ForcesForces

Page 2: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

The Nature of ForceThe Nature of Force By definition, a By definition, a ForceForce is a is a pushpush or a or a pullpull..

A Push

Or

A Pull

Just like Velocity & Acceleration Forces have

both magnitude and direction

components

Just like Velocity & Acceleration Forces have

both magnitude and direction

components

Page 3: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Balanced & Unbalanced Balanced & Unbalanced ForcesForces

With a Balanced force – opposite and equal forces acting on the same object result in NO motion of the object

Unbalanced forces Unbalanced forces – two or more forces of unequal – two or more forces of unequal strength or direction acting upon on an object strength or direction acting upon on an object results results in the motion of the objectin the motion of the object

Page 4: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

VectorsVectors Vectors are a method used to visually show forcesVectors are a method used to visually show forces A A vectorvector is a quantity which has both magnitude (size) and direction. is a quantity which has both magnitude (size) and direction.

The The lengthlength of the arrow shows the of the arrow shows the magnitudemagnitude of the vector. of the vector. The The angleangle of the arrow shows the vector's of the arrow shows the vector's directiondirection..

Just like numbers, we can add two or more vectors together Just like numbers, we can add two or more vectors together and get a and get a net force net force called the called the resultantresultant

Page 5: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Adding 2 or More Adding 2 or More VectorsVectors

Add vectors A and B to get the Resultant C Add vectors A and B to get the Resultant C A + B = CA + B = C

Fig 1 - shows the magnitude & direction of the 2 vectors we are addingFig 1 - shows the magnitude & direction of the 2 vectors we are adding Fig 2 – we move the beginning of vector B to the end of Vector A, making sure to keep the magnitude & direction exactly Fig 2 – we move the beginning of vector B to the end of Vector A, making sure to keep the magnitude & direction exactly

the samethe same Fig 3 – Connect the beginning of Vector A to the end of Vector B, this is your “Resultant” C.Fig 3 – Connect the beginning of Vector A to the end of Vector B, this is your “Resultant” C.

Fig 1

Fig 2

Fig 3

Click the icon to run java script game that

allows you to add vectors

Page 6: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Newton’s 3 Laws of Newton’s 3 Laws of MotionMotion

Newton’s 1st Law of MotionNewton’s 1st Law of Motion: : AKA AKA The Law of Inertia The Law of Inertia

which states which states an object at rest will remain at rest, and an an object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity object in motion will remain in motion at a constant velocity until acted on by another force.until acted on by another force.

Remember: The greater the mass of an object the greater the inertia

Page 7: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Newton’s Second Law of Motion Newton’s Second Law of Motion aka aka F=maF=ma Force = mass x accelerationForce = mass x acceleration

Can be written as:Can be written as: F=ma ; a= F/m ; m= F/aF=ma ; a= F/m ; m= F/a

What is the basic unit for mass? What is the basic unit for mass? KilogramKilogram What is the basic unit for acceleration? What is the basic unit for acceleration? Meter/secMeter/sec22

Therefore the basic unit for Force is Therefore the basic unit for Force is

(kilogram)( meter/sec(kilogram)( meter/sec22)) An object with a mass of 1 kg accelerating at 1 m/sAn object with a mass of 1 kg accelerating at 1 m/s22 has a has a

force of 1 Newton force of 1 Newton

Newton’s 3 Laws of Newton’s 3 Laws of MotionMotion

Page 8: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Newton’s 2Newton’s 2ndnd Law & Force of Law & Force of GravityGravity

Everyone has heard of the FORCE of gravityEveryone has heard of the FORCE of gravity

So far, we know only of four types of So far, we know only of four types of fundamental forcesfundamental forces in nature:in nature:

Gravity, Electromagnetic, Weak, and StrongGravity, Electromagnetic, Weak, and Strong Gravity: the force that pulls objects towards each otherGravity: the force that pulls objects towards each other Since gravity is a force it also obeys Newton’s second lawSince gravity is a force it also obeys Newton’s second law

F=maF=ma

With this experiment, Galileo proved Aristotle wrong

Since objects fall at the same speed, their

acceleration is the same.All objects accelerate at

the rate. Here on Earth the rate is:

Ag=9.8 m/s2

OrAg=32 ft/s2

With this experiment, Apollo 15 astronauts proved Galileo right.(link to You Tube)

Air resistance keeps things from falling equally

Page 9: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

F=maF=ma Weight is the force of gravity acting on an object’s mass.Weight is the force of gravity acting on an object’s mass. Therefore weight is a type of ForceTherefore weight is a type of Force The formula for weight: Weight = mass x AThe formula for weight: Weight = mass x Agg

SinceSince A Agg= 9.8 m/s= 9.8 m/s2 2 then then

Weight = mass x 9.8 m/sWeight = mass x 9.8 m/s22

Newton’s 2Newton’s 2ndnd Law & Weight Law & Weight

Remember:1 newton = 0.22 pounds

Page 10: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Your weight Your weight on other on other planetsplanets

& 3 different & 3 different types of types of

starsstars

Page 11: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Newton’s 3Newton’s 3rdrd Law of Motion Law of Motion:: For every action there is an equal & opposite reaction.For every action there is an equal & opposite reaction.

If an object is not in motion, then all forces acting on it are balanced and the net force is zero!If an object is not in motion, then all forces acting on it are balanced and the net force is zero! Friction – the force that one surface exerts on another when the two rub against each other.Friction – the force that one surface exerts on another when the two rub against each other.

Newton’s 3 Laws of Newton’s 3 Laws of MotionMotion

Sliding friction

Rolling friction

Fluid friction

Page 12: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Momentum Momentum An object’s momentum is directly related to both its An object’s momentum is directly related to both its

mass and velocity.mass and velocity. Momentum = mass x velocity Momentum = mass x velocity For some reason, maybe because mass is designated as For some reason, maybe because mass is designated as

“m” in formulas, momentum is designated as ““m” in formulas, momentum is designated as “pp”. ”.

Therefore: Therefore: pp = mv = mv The unit for The unit for mass is kgmass is kg, the unit for , the unit for velocity is velocity is

meter/secondmeter/second, therefore the unit for momentum is kg , therefore the unit for momentum is kg m/secm/sec

Conservation of MomentumConservation of Momentum:: When two or more objects interact (collide) the total momentum When two or more objects interact (collide) the total momentum

before the collision is equal to the total momentum after the before the collision is equal to the total momentum after the collisioncollision

Page 13: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Momentum – 2 moving Momentum – 2 moving objectsobjects During this collision the speed of both box cars During this collision the speed of both box cars

changes. The total momentum remains constant changes. The total momentum remains constant before & after the collision. The masses of both cars before & after the collision. The masses of both cars is the same so the velocity of the red car is is the same so the velocity of the red car is transferred to the blue car.transferred to the blue car.

Page 14: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Momentum – 1 moving Momentum – 1 moving objectobject During this collision the speed red car is transferred During this collision the speed red car is transferred

to the blue car. The total momentum remains to the blue car. The total momentum remains constant before & after the collision. The masses of constant before & after the collision. The masses of both cars is the same so the velocity of the red car is both cars is the same so the velocity of the red car is transferred to the blue car.transferred to the blue car.

Page 15: Physical Science Forces. The Nature of Force By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. A Push Or A Pull

Momentum – 2 Momentum – 2 connected objectsconnected objects After this collision, the coupled cars make one object After this collision, the coupled cars make one object

w/ a total mass of 60,000 kg. Since the momentum w/ a total mass of 60,000 kg. Since the momentum after the collision must equal the momentum before, after the collision must equal the momentum before, the velocity must change. In this case the velocity is the velocity must change. In this case the velocity is reduced from 10 m/sec. to 5 m/sec. reduced from 10 m/sec. to 5 m/sec.