 # FORCE AND MOTION IF ENERGY IS THE ABILITY TO DO WORK AND WORK IS THE APPLYING OF A FORCE TO AN OBJECT TO MAKE IT MOVE (MOTION). WHAT IS MOTION? WHAT IS.

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FORCE AND MOTION IF ENERGY IS THE ABILITY TO DO WORK AND WORK IS THE APPLYING OF A FORCE TO AN OBJECT TO MAKE IT MOVE (MOTION). WHAT IS MOTION? WHAT IS A FORCE?

MOTION:  Event that involves a change in the position or location of something.  Motion is relative—It is described compared to a reference point.  Factors that affect an object’s motion; amount of force, duration of force, surface, and mass of the object.

FORCE:  A force is a push or a pull on an object. A force transfers energy to an object, causing it to; start moving, stop moving, change directions, or change shape.  Measured in Newtons (N)  Tool—Use a Spring Scale  Forces have both strength and direction.

….CONTINUED  As these forces act upon objects, the objects move depending on the force being balanced or unbalanced.  Balanced—all forces acting on an object are equal—there is NO motion.  Unbalanced—one or more forces acting on an object are stronger than the others—there IS motion and therefore a net force.

FORCES CAN BE COMBINED OR ACT IN OPPOSITE DIRECTIONS. NET FORCE IS THE COMBINATION OF FORCES. Applied ForceNet force = = 0 N = 5N5N 5N5N 10 N 5N5N 5N5N 5N

Balanced Force 10 NEWTONS Net Force = 0 N The ball will not move

Unbalanced Force Net Force = 10 N The ball will move to the left 10 NEWTONS 20 NEWTONS

2 TYPES OF FORCES (OR PUSH AND PULL): 1. Contact Force:  A push or a pull on one object by another object that is touching it.  Contact forces may be weak or strong.  Examples include; Applied, Normal, Air Resistance, Tension, Spring and Friction Box Gravity Normal Force 90 0

Applied Force Tension Friction

FRICTION  A force that resists the motion of two surfaces that are touching.  Types:  Static—Objects in contact but not moving.  Sliding—Objects that slide over each other.  Rolling—Objects that roll over each other.  Fluid—Objects that move across or through a fluid.

…CONTINUED  Cause? Microscopic dips and bumps that cover all surfaces.  Results—Good—brakes, shoes, pencils—Bad—Engine damage, tire wear, causes surfaces to heat up and wear away.  Decrease—  Use of lubricants by making the surface smoother. Oil, grease, water, etc.  Aerodynamics—make a surface smoother in fluids. Shape of rocket, biking helmet..etc.

2. NONCONTACT (AT-A-DISTANCE) FORCE:  A force that one object can apply to another object without touching.  Gravity—An attractive force that exists between all objects that have mass. The strength of the force depends on the mass of the each object and the distance between them.  Magnetic—Attraction of certain metals to magnets.  Electric– Attraction between charged particles. - + + + --

NEWTON’S 3 LAWS OF MOTION: DESCRIBES MOTION AND CHANGES IN MOTION AS RELATED TO A FORCE.  1st: If the net force of an object is zero, the motion of the object does not change.  Inertia—The tendency of an object to resist a change in its motion.  The more mass an object has, the more inertia the object has.  Bigger objects are harder to start & stop

 2nd: The acceleration of an objects is equal of the net force acting on the object divided by the object’s mass.

 3rd: When on object exerts a force on a second object, the second object exerts a force of the same size but in the opposite direction on the first object.

The truck is in motion. What is the force that causes it to stop? The push of the stopped car. The car is at rest. What is the force that causes it to move? The push of the truck.

What about the ladder on top of the truck? The ladder is in motion because the truck is in motion. When the truck stops, the ladder stays in motion. The truck is stopped by the force of the car, but the ladder is not. What force stops the ladder? Gravity.

The truck is in motion, the car is at rest. How do each of these vehicles accelerate? The truck stops moving. The car starts moving. Which one will be the hardest to accelerate? The truck because it has the most mass.

 Why does the car move [accelerate] when it is hit by the truck?  The heavy and moving truck has more force than the small, at rest car.  Why does the truck stop moving when it hits the car?  The force of the car pushing back on the truck, plus the force of friction between the massive truck and the road slow down, the stop the truck.

 The truck hits the car. An action force stops the truck.  What is the equal and opposite reaction force?  The force that pushes the car forward.

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