Section 1 Gravity and Motion

Section 2 Newton’s Laws of Motion

Section 3 Momentum

• Gravity and Acceleration

Objects fall to the ground at the same rate because the acceleration due to gravity is the same for all objects.

• Acceleration Due to Gravity

The object’s downward velocity increases by 9.8 m/s.

Gravity and Falling Objects

Iron ballWood ball

Acceleration of gravity is independent of the mass of the falling object!

• Velocity of Falling Objects You can calculate the change in velocity with

the following equation:

¨ ∆v = g X t

• If an object starts at rest, this equationyields the velocity of the object after a certain time period.

• Air resistance is the force that opposes the motion of objects through air.

• The amount of air resistance acting on an object depends on the size, shape, and speed of the object.

Air Resistance and Falling Objects

¨ As the 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. The object then falls at a constant velocity called the

terminal velocity.

¨ An object is in free fall :- When There Is No Air Resistance- only if gravity is pulling it down and

no other forces are acting on it.

A vacuum is a place in which there is no matter. Objects falling in a vacuum are in free fall because there is no air resistance.

¨ Astronauts float in orbiting spacecrafts because of free fall.

¨ Orbiting and Centripetal Force

The unbalanced force that causes objects to move in a circular path is called a centripetal force.

Gravity provides the centripetal force that keeps objects in orbit.

Too slow => Object falls back down to Earth

Too fast => Object escapes Earth’s gravity

¨ Projectile motion is the curved path an object follows when it is thrown or propelled near the surface of the Earth.

¨ Projectile motion has two components that are independent of each other;;

-­ horizontal velocity-­ vertical velocity

1.A body continues at rest or in uniform motion in a straight line unless acted upon by some net force.

An astronaut floating in space will continue to float forever in a straight line unless some external forceis accelerating him/her.

¨ Friction between an object and the surface it is moving over is an example of an unbalanced force that stops motion.

¨ Inertia is the tendency of all objects to resist any change in motion.

¨ Mass is a measure of inertia. - Small mass has less inertia- Large mass has greater

inertiaNewton’s first law is sometimes called

the law of inertia.

¨ The acceleration of an object depends on the mass of the object and the amount of force applied

a = F/m ó F = m a

¨ Part 1: Acceleration Depends on Mass The acceleration of an object decreases as its mass increases.

¨ Part 2: Acceleration Depends on Force An object’s acceleration increases as the force on the object increases.

¨ The acceleration of an object is always in the same direction as the force applied.

¨ Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

To every action, there is an equal and opposite reaction.

All forces act in pairs.

¨ Force Pairs Do Not Act on the Same Object.¨ When a force is exerted, there is always a reaction force.A force is always exerted by one object on another object.

• The momentum of an object depends on the object’s mass and velocity.

P = m x v

¨ The law of conservation of momentum states; - that any time objects collide, the

total amount of momentum stays the same.- After two objects stick together, they

move as one object - The combined objects have a

different velocity because momentum is conserved and depends on mass and velocity.

• So, when the mass changes, the velocity must change, too.

Objects Bouncing Off Each Other • When two objects bounce off each other,

momentum is transferred from one object to the other.

• The transfer of momentum causes the objects to move in different directions at different speeds.

¨ Because action and reaction forces are equal and opposite, momentum is neither gained or lost in a collision