Forces in MotionForces in Motion

Chapter 2 NotesChapter 2 Notes

Part 1Part 1

QuestionsQuestions• How does the force of gravity

affect falling objects?

• What is projectile motion?

• What are Newton’s laws of motion?

• What is momentum?

Falling ObjectsFalling Objects• Mass of an object does not

affect the rate at which it falls.

• All objects fall with the same acceleration rate due to gravity. (9.8 m/s/s on Earth)

Air ResistanceAir Resistance

• definition – fluid friction that opposes the motion of objects as they pass through the air.

• Acts to slow down acceleration.

• Will affects some objects more than others due to their size and shape.

Affects of air resistance on Affects of air resistance on downward acceleration of downward acceleration of a falling objecta falling object

The force of air resistance

Net force on the object

The force of gravity

http://www.cirrusdesign.com:4515/pilotsworld/images/intro/grabber_11_05.swf

Terminal VelocityTerminal Velocity• As speed the amount of air resistance

• As the object falls, upward forces of air resistance increases until they equal the downward force of gravity

• Net force is zero

• Objects stops accelerating

• Object falls at constant velocity, which is called its terminal velocity.

Free fallFree fall

• Occurs when there is no air resistance.

• Only force acting on the object is the force of gravity.

OrbitingOrbiting• Objects are in Free Fall

• Two motions combine to cause orbiting

– Moving forward

– Free fall toward Earth

– Causes centripetal (center seeking) force

Projectile MotionProjectile Motion

• definition: The curved path an object follows when thrown or propelled near the surface of the Earth.

Projectile MotionProjectile Motion• Caused by two independent forces:

–Horizontal – the force applied to move it forward. Causes motion parallel to the ground.

–Vertical – gravity pulling on the object. Causes motion perpendicular to ground.

ExplainExplain

• Explain why a ball moves in a straight lines as it rolls across a table but follows a curved path once it rolls off the edge of the table.

History of Newton’s LawsHistory of Newton’s Laws

Sir Isaac Newton (1643-1727) an English Sir Isaac Newton (1643-1727) an English scientist and mathematician famous for scientist and mathematician famous for his discovery of the law of gravity also his discovery of the law of gravity also discovered the three discovered the three laws of motionlaws of motion..

Today these laws are known as Today these laws are known as Newton’s Newton’s Laws of MotionLaws of Motion and describe the motion and describe the motion of all objects on the scale we experience of all objects on the scale we experience

in our everyday lives.in our everyday lives.

“If I have ever made any valuable discoveries, it has been owing more to patient attention, than to any other talent.”

-Sir Isaac Newton

Newton’s 3 Laws of MotionNewton’s 3 Laws of Motion• An object in motion tends to stay in

motion and an object at rest tends to stay at rest unless acted upon by an unbalanced force.

• Force equals mass times acceleration (F = ma).

• For every action there is an equal and opposite reaction.

MomentumMomentum

• Momentum is a property of moving objects.

• Amount depends on the objects mass and velocity.

• Formula: p = m x v momentum = mass x velocity

Conservation of MomentumConservation of Momentum

• When two or more objects interact, momentum may be transferred, but the total amount of momentum does not change. This is known as the

“ Law of Conservation of Momentum”.