Gravity and Motion

• Aristotle (400BCE) – rate of acceleration depended on mass

• Galileo (late 1500’s) – mass of an object does not affect the rate at which an object falls

• Why? Acceleration depends on force and mass

• Heavier object experiences greater force of gravity, however, it takes more force to accelerate

• Heavier mass balances additional force of gravity so all objects will fall at same rate

• Acceleration – rate at which velocity change over time (either speed or direction)

• All objects accelerate toward earth at 9.8m/s2. which means…

• For every second object falls, downward velocity increases by 9.8 m/s

• Air resistance – force that opposes motion through air

• Air resistance depends on size, shape and speed

• Speed of a falling object increases, air resistance increases

• The upward force of air resistance continues to increase until it is equal to the downward force of gravity and the net force = 0, the object stops accelerating

• Terminal velocity – constant velocity of a falling object

• Free fall – happens only when gravity is acting on an object (no air resistance)

• Vacuum – place where there is no matter (space)

• Orbit – forward motion with a change in velocity (direction)

• Centripetal force – force that causes objects to move in a circular path

• Projectile motion – curved path that an object follows when thrown, launched or otherwise projected near the earths surface – consists of horizontal and vertical motion

• Inertia – the tendency of all objects to resist any change in motion

• Mass is a measure of inertia – the greater the mass the greater force of inertia

• Newton’s First Law of Motion – Law of inertia

– An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force

• Acceleration depends on mass – as mass increases, the amount of force need to accelerate an object increases

• Acceleration of an object is always in direction of the force applied

• Newton’s Second Law of Motion –– The acceleration of an object depends on the mass of

the object and the amount of force applied.

Formula: F= m x a

Units for Calculation

• Force = N (newton)

• Mass = Kg

• Acceleration = m/s2

• Newton’s Third Law of Motion– Whenever one object exerts a force on a

second object the second object exerts an equal and opposite force on the first object

• Sometimes called the “action / reaction” law

• States that all forces work in pairs.

• Momentum – product of the mass and velocity of an object ( p = m x v )

• The Law of Conservation of Momentum– Momentum can not be gain or lost only

transferred– Any time objects collide, the total amount of

momentum stays the same. (Newton’s 3 law)

Identify the Law