Download Motion, Force, Gravity, Projectile Motion and Friction NYS Standards

Motion, Force, Gravity, Projectile Motion and Friction
NYS Standards:
5.1a The motion of an object is always judged with respect to some other object or point. The idea of
absolute motion or rest is misleading.
5.1b The motion of an object can be described by its position, direction of motion, and speed.
5.1c An objects motion is the result of the combined effect of all forces acting on the object. A moving
object that is not subjected to a force will continue to move at a constant speed in a straight line. An
object at rest will remain at rest.
5.1d Force is directly related to an objects mass and acceleration. The greater the force, the greater the
change in motion.
5.1e For every action there is an equal and opposite reaction.
5.2a Every object exerts gravitational force on every other object. Gravitational force depends on how
much mass the objects have on how far apart they are. Gravity is one of the forces acting on orbiting
objects and projectiles.
Motion
-When an object changes position over time when compared with a reference point.
Object in motion 
 Reference Point
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There are three ways to categorize motion.
o Position
o Direction of Motion
o Speed
The direction of the objects motion is dependent on the reference point.
If the reference point changes, the direction of the object can also be looked at differently.
Force
-A push or pull on an object.
 There are three characteristics of forces.
o Have size
o Direction
o Units = Newtons (N)
 Ex: 40.0 N West

If an object is moving or even if it is sitting still, there are still forces acting upon it.
o If the forces acting on the object are balanced, or equal to one another but in opposite
directions…then the object doesn’t move.
o If one of the forces is larger, it will move the object in the direction of the force.

Force Diagrams
o 1. If the forces are moving in the same direction, you add the forces together.
o 2. If the forces are moving in the opposite direction, you subtract them, leaving the
object to move in the direction of the greater force.
o Example 1: Are the forces acting on this object balanced or unbalanced? What is the net
force acting on the object? What direction is the object going to move?
Net Force = 10.0N East + 50.0N East
Net Force = 60.0 N East, the object is unbalanced
o Example 2: Are the forces acting on this object balanced or unbalanced? What is the net
force acting on the object? What direction is the object going to move?
Net Force = 75.0N West - 35.0N East
Net Force = 40.0 N West, the object is unbalanced
o Example 3: Are the forces acting on this object balanced or unbalanced? What is the net
force acting on the object? What direction is the object going to move?
Net Force = 20.0N West - 20.0N East
Net Force = 0.0 N the object does not move, the object is balanced
Newton’s Three Laws of Motion
1. An object in motion tends to stay in motion (or an object at rest tends to stay at rest) unless acted upon by an
outside fore. Also called The Law of Inertia.
 Inertia – The tendency of all objects to resist any change in motion.
2. Force = mass x acceleration
Example: An object has a mass of 50.0kg and moves with an acceleration of 5.0m/s2. What is the amount of
force the object has?
F = mass x acceleration
F = 50.0kg x 5.0m/s2
F = 250.0 N
3. For every action, there is an equal and opposite reaction.
Gravity
-Gravity is a force of attraction that exists between all objects in the universe.
 The pull of gravity is directly related to mass. As the mass of an object increases, the
gravitational force increases.

The pull of gravity is also related to distance between objects. As the distance between two
objects decreases, the gradational force increases.

The direction of Earth’s gravitational pull is toward the center of Earth.
Projectile Motion
-The curved path an object follows when thrown or propelled near the surface of the Earth.
-Examples: Throwing a ball, arrows shot from a bow, a leaping grasshopper, a catapult, and shooting a
basket.

Two Components
o Horizontal Motion – Motion that is parallel to the ground.
o Vertical Motion - Motion that is perpendicular to the ground
o Both motions combine to form a curved path.
Friction
-A force that opposes motion between two surfaces that are touching.
-There is NO SUCH THING as a completely smooth surface.
-Heat is the most common form of energy that results from friction. The greater the friction, the
greater the heat generated.

The Source of Friction
o There are microscopic hills and valleys on the
surface of every object. As the surfaces move back
and forth, the hills and valleys stick to one another.

What Controls the Amount of Friction
o 1. Roughness of surfaces
 Rougher the surface = more friction
o 2. Force pushing the objects together
 Greater the force = more friction

Four Types of Friction
o 1. Sliding Friction
 Requires a great amount of force to move the object. There is a large amount of
opposing force.
o 2. Rolling Friction
 Requires much less force to move the object. There is a small amount of
opposing force.
o 3. Static friction
 the friction that acts on objects that are not moving
 Ex: Moving a desk. It takes more force to get it moving (overcome static friction)
o 4. Fluid Friction: when an object moves through a fluid
 Ex: Biking, surfing, swimming.

How Can We Increase or Decrease Friction?
o Decrease Friction
 Lubricants – Substances that are applied to surfaces to reduce friction between
them.
 Examples – Oils, Waxes, Greases, and Water.
o Increase Friction
 1. Increase the force acting on the object.
 2. Increase the roughness of the surface.
 Examples – Paperweights, Sand on roads, and Sanding surfaces.