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Friction and Gravity (Friction (The Causes of Friction (Smoother surfaces…

- - - - "The strength of force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved."
        
        Friction increases if surfaces are pushed hard against each other.
        
        Friction occurs when the irregularities of one surface comes into contact with those of another surface.
        
        Friction acts in the opposite direction to the direction of the object's motion
  - - - “Because of static friction, you must use extra Force to start the motion of stationary objects.”
        
        Once moving there is no more static friction.
  - - - Sliding friction acts when you add sand to ice or put your brakes on to stop your bike.
  - - - “Rolling friction is easier to overcome in sliding friction for similar materials.”
        
        When is skateboarder is riding their skateboard the rolling friction acts in the direction opposite to the skateboarders motion.
  - - - Fluid friction is easier to overcome than rolling friction and sliding friction.
        
        For example, fluid friction can occur between you in the air when you ride your bike or between a surfboard and the water.
- - - - Isaac Newton discovered the law of universal gravitation, which says that the force of gravity acts between all objects in the universe.
        
        This means that any two objects in the universe attract each other without exception.
        
        You're attracted to the Earth but also to all the other objects around you.
        
        The objects around you and the Earth are also attracted to you, but you don't notice the attraction among objects because these forces are small compared to the force of the Earth's attraction.
  - - - Mass is a measure of the amount of matter in an object and the SI unit of mass is the kilogram. One kilogram is the mass of about 400 modern pennies and everything that has mass is made up of matter.
        
        The more mass an object has, the greater its gravitational force is because the Sun's mass is so great that it exerts a large gravitational force on the planets and that is one of the reasons why the planets orbit the Sun.
        
        Gravitational force depends on the distance between the objects and the farther apart two objects are the less the gravitational force is between them.
  - - - The force of an object on the surface of a planet or gravity on a person is known as weight.
        
        Weight will vary with the strength of the gravitational force but mass does not.
- - - - Objects accelerate near the surface of the Earth, the acceleration due to gravity is 9.8 m/s squared And this means that for every second an object is falling, its velocity increases by 9.8 m/s.
        
        All objects in free-fall accelerate at the same rate regardless of their masses.
  - - - Objects that fall through air experience a type of fluid friction called air resistance.
        
        Friction is in the direction opposite to emotion, so air resistance is not an upward force exerted on falling objects.
        
        Air resistance is not the same for all objects and falling objects with a greater surface area experienced more air resistance.
        
        Air resistance increases with velocity.
        
        As an object falling speeds up, the force of air resistance becomes greater and greater.
        
        Eventually, the falling object will fall fast enough that the upward force of air resistance becomes equal to the downward force of gravity acting on the object and it is at this point that The forces on the object are balanced.
        
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  - - - An arrow flying toward a target is a projectile because of the force of gravity, the arrow will fall as it flies toward the target. If you try to hit the bullseye you must aim above the bull's-eye to account for its gravity's pull.
        
        When you throw a projectile at an upward angle, the force of gravity reduces its vertical velocity and eventually, the upward motion of the projectile will stop, therefore the gravity will pull it backwards towards the ground. Is at this point that the projectile will fall at the same rate as any dropped object.