Chapter 6

Forces in Motion

6-1 Gravity and Motion

• Objects Falling– All objects fall with

the same acceleration

– Gravity Constant• 9.8 m/s2 on Earth

• To fin the Velocity of an object you must use this equation

• V = g * t

6-1 Gravity and Motion

• Find the Velocity of a penny that is dropped after it falls for 2 seconds

• A rock hits the ground after falling for 4.5 seconds, what is the velocity?

6-1 Gravity and Motion

• Air Resistance– fluid friction between

the air and the object

– slows down acceleration

– will affect objects differently

6-1 Gravity and Motion

• Terminal Velocity– the point where

acceleration stops

– the upward force of air resistance matches the downward force of gravity

• = a net force of 0 N

6-1 Gravity and Motion

• Free Fall– occurs with no air

resistance

– all objects will fall at same acceleration

6-1 Gravity and Motion

• Orbiting Objects– are in free fall

– object moves forward but is pulled by a larger object

– smaller object path is curved by gravity of larger object

6-1 Gravity and Motion

• Orbiting Objects– centripetal force

• unbalanced force that causes object to move in a circular path

• constantly changing direction there for is always accelerating

6-1 Gravity and Motion

• Projectile Motion– the curved path an

object follows when thrown or propelled near the surface of the Earth

– 2 Components• Horizontal Motion

• Vertical Motion

6-1 Gravity and Motion

• Projectile Motion– Horizontal Motion

• the motion that is parallel to the ground

• Baseball– once you throw the

ball there is now more horizontal force on the ball

– ball’s horizontal velocity is constant once it leaves your hand

6-1 Gravity and Motion

• Projectile Motion– Vertical Motion

• the motion perpendicular to the ground

• acts on all falling objects

6-2 Newton’s Laws of Motion

• Newton’s First Law of Motion (Law of Inertia)– States that an object at rest

will remain at rest and an object that is moving at constant velocity will continue moving at constant velocity unless acted upon by an unbalanced force

6-2 Newton’s Laws of Motion

• Friction– The unbalanced force

that will stop motion– Will change the

motion of an object in the direction of the friction

6-2 Newton’s Laws of Motion

• Newton’s First Law of Motion (Law of Inertia)– Inertia

• The tendency of an object to resist change in its motion

• The greater the mass the greater the inertia

• The greater the velocity the greater the inertia

6-2 Newton’s Laws of Motion

• Newton’s Second Law of Motion– The net force on an object is equal to the product of its

acceleration and its mass

6-2 Newton’s Laws of Motion

• Newton’s Second Law of Motion– Force = Mass x Acceleration

• Unit is the Newton (N)=kg x m/s2

– Acceleration = Force / Mass

– A 68 kg water-skier is being pulled by a speedboat. The force causes her to accelerate at 2 m/s2. Calculate the net force that causes this acceleration.

• Force = Mass x Accel• Force = 68 kg x 2 m/s2

• Force = 136 kg x m/s2

• Force = 136 N

6-2 Newton’s Laws of Motion

• Changes in Force and Mass– How to change

acceleration?• If Force goes up accel

goes up• If force goes down accel

goes down• If mass goes up accel

goes down• If mass goes down accel

goes up