# chapter 8 section 3 notes motion and force. what is force? force □a force is the cause of...

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• Slide 1
• Chapter 8 Section 3 Notes Motion and Force
• Slide 2
• What is Force? force A force is the cause of acceleration or change in an objects velocity
• Slide 3
• Fundamental Forces 4 fundamental forces There are 4 fundamental forces in nature: Gravity Electromagnetic force Strong nuclear force Weak nuclear force
• Slide 4
• Fundamental Forces Gravity: very, very weak force; this force acts over a long distance; much weaker than the electromagnetic force; field force Electromagnetic force: moderate force; acts over long distances; about 1/100 the strength of the strong force; field force
• Slide 5
• Fundamental Forces Strong nuclear force: strongest of all forces, but acts over a very short distance; only acts over distances the size of the atomic nucleus Holds together protons and neutrons in the nuclei of atoms Weak nuclear force: associated with nuclear decay
• Slide 6
• Fundamental Forces
• Slide 7
• Types of Forces Contact forces: caused when objects touch Examples: when you push a shopping cart or catch a baseball and it stops moving Field forces: do not require that objects touch each other Examples: attraction of gravity or repulsion between 2 north poles of a magnet Both contact and field forces can cause an object to move or stop moving!
• Slide 8
• Balanced and Unbalanced Forces Net force: the sum of all the forces acting on an object Whenever there is a net force acting on an object, the object accelerates in the direction of the net force.
• Slide 9
• Balanced and Unbalanced Forces An object will not accelerate if the net force is equal to zero. Balanced forces: net force of zero Do not cause a change in motion of an object.
• Slide 10
• Balanced and Unbalanced Forces Example of Balanced Forces: When 2 teams are playing tug of war and both teams are exerting equal amounts of pressure, there is no acceleration, and neither team moves.
• Slide 11
• Balanced and Unbalanced Forces Unbalanced forces: occurs when forces acting on an object dont cancel out; there is a greater force acting on 1 side of the object Example: When 2 teams are playing tug of war and one team exerts a greater force and pulls the other team forward
• Slide 12
• Balanced and Unbalanced Forces When an object is at rest, are there still forces acting on it? Yes! It is just not moving because the forces are balanced. What happens if forces act in different directions that are not opposite one another? The combination of forces acts like a single force and cause acceleration in a combined direction Example: You push your book east and your friend pushes the book north; the book will move northeast
• Slide 13
• Friction Friction: force between 2 objects that opposes the motion of either object Example: Imagine a car rolling on a flat, evenly paved street. Eventually, the car will stop due to the force of friction. Friction depends on surfaces in contact: Frictional forces are greater when both surfaces are rough Example: new tennis shoes walking along a carpeted floor will keep you from falling down.
• Slide 14
• Friction Two types of friction: Static Friction: when 2 objects touch but do not move Example: A filing cabinet sitting on the floor
• Slide 15
• Friction Kinetic Friction: friction between moving surfaces. Two types of kinetic friction: Sliding friction: when 1 object slides over another Example: Sliding a box across the counter Rolling friction: when 1 object rolls across another Example: Rollerblading
• Slide 16
• Friction The force necessary to make a stationary object start moving is usually more than the force necessary to keep it moving; therefore, static friction is usually greater than kinetic friction. Rolling friction is usually less than sliding friction.
• Slide 17
• Friction and Motion Friction is not all bad; it is actually required for many everyday tasks to work correctly. Examples: Cars could not move without friction; as a cars wheels turn, they push against the road and as a reaction, the road pushes forward on the car. You would not be able to write down these notes either!
• Slide 18
• Friction and Acceleration
• Slide 19
• Air Resistance Air Resistance: a type of friction Air Resistance is caused by the interaction between the surface of a moving object and the air molecules Air Resistance depends on 3 factors: Size of the object Shape of the object Speed of the object
• Slide 20
• Gravity Gravity: force of attraction between 2 particles of matter due to their mass Gravity is different from other forces because: gravity acts on an object even when the objects dont touch All objects in the universe attract each other through the force of gravity!
• Slide 21
• Gravity Gravity depends on two factors: The mass of the objects: the greater the mass of the object, the larger the gravitational force The distance between the objects: as the distance between 2 objects increases, the gravitational force decreases.