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Chapter 10

Chapter 10. Forces. Force. When one object pushes or pulls another object, the first object exerts a force on the second object. A force is described by its strength and by the direction in which it acts. Strength of a force is measured in Newtons (N). Arrows.

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Chapter 10

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  1. Chapter 10 Forces

  2. Force • When one object pushes or pulls another object, the first object exerts a force on the second object. • A force is described by its strength and by the direction in which it acts. • Strength of a force is measured in Newtons (N)

  3. Arrows • The direction and strength of a force is represented by an arrow. • The arrow points in the direction of the force. • The longer the arrow, the greater the force.

  4. Net Force • The combination of all forces acting on an object is called the Net Force. • Net force determines whether an object moves and also in which direction it moves.

  5. Unbalanced Forces • Whenever there is a net force acting on an object, the forces are unbalanced. • Can cause an object to start moving, stop or change direction. • Unbalanced forces acting on an object results in a net force and cause a change in the object’s motion.

  6. Balanced Forces • Equal forces acting on one object in opposite directions are called Balanced Forces. • Each force is balanced by the other. • Balanced forces acting on an object do not change the object’s motion.

  7. Friction • The force that two surfaces exert on each other when they rub against each other is called Friction.

  8. Cause of Friction • The strength of the force of friction depends on two factors: • How hard the surfaces push together. • The types of surfaces involved.

  9. Types of Friction • Static Friction • The friction that acts on objects that are not moving. • Pushing a heavy object. • Sliding Friction • Occurs when two solid surfaces slide over each other • Rubber pads stopping a bicycle tire.

  10. Types of Friction • Rolling Friction • When an object rolls across a surface. • Ball bearings reduce rolling friction in skateboards. • Fluid Friction • Occurs when a solid object moves through a fluid (water, oil or air). • Air that flows over a cyclist is fluid friction.

  11. Gravity • Gravity is a force that pulls objects toward each other.

  12. Factors affecting Gravity • Two factors affect the gravitational attraction between objects: • Mass- The amount of matter in an object. • Distance- The further two objects are, the lesser the gravitational force.

  13. Gravity and Motion • Free Fall- When the only force acting on an object is gravity, the object is said to be in Free Fall. • In free fall, the force of gravity is an unbalanced force, which causes an object to accelerate. • Acceleration due to gravity- 9.8 m/s2

  14. Air Resistance • Fluid friction that objects experience as they fall through the air. • Terminal Velocity- The greatest velocity a falling object reaches. • Reached when the upward force of air resistance cancels the downward force of gravity.

  15. Projectile Motion • An object that is thrown is called a Projectile. • A projectile will fall at the same rate as a dropped object.

  16. Newton’s First Law of Motion • An object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force.

  17. Inertia • The tendency of an object to resist a change in motion. • The greater the mass of an object, the greater its inertia.

  18. Newton’s Second Law of Motion • Acceleration depends on the object’s mass and on the net force acting on the object. • Net Force (Fnet) = Mass (Kg) x Acceleration (m/s2) • The units for Net Force is Newton (N).

  19. Changes in Force and Mass • How do you increase the acceleration of an object? • Change the force on the object • Change the mass of the object

  20. Newton’s Third Law of Motion • If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. • For every action there is an equal but opposite reaction.

  21. Action-Reaction • Action- Jumping from the ground with your feet. • Reaction- The ground pushes back on your feet with equal and opposite force. • These forces do not cancel because they are acting on different objects.

  22. Momentum • The product of an object’s mass and velocity. • You can determine the momentum of a moving object by multiplying the object’s mass and velocity. • Momentum = Mass x Velocity • The units for momentum is Kg•m/s

  23. Momentum • The more momentum a moving object has, the harder it is to stop. • The greater the mass, the greater an object’s momentum. • The greater the velocity, the greater an object’s momentum.

  24. Conservation of Momentum • In the absence of friction, momentum is conserved when two objects collide. 4 m/s 2 m/s Before 2 m/s 4 m/s After

  25. Centripetal Force • Any force that causes an object to move in a circular path.

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