# The Nature of Forces. Force a push or pull that gives energy to an object sometimes causes a change in motion.

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The Nature of Forces

Force a push or pull that gives energy to an object sometimes causes a change in motion

To describe a force you need to know two things:  The direction  The strength Used to draw Force Diagrams

Units of Force English – pounds (lb) (That’s right. Your weight is a force, not a measure of mass.) Metric – newtons (N) One pound is about 4.5 N.

Forces can give energy to objects, sometimes causing them to: start moving stop moving change direction

The combination of all forces acting on an object Net Force

Equal and opposite (balanced) forces produce NO motion. NO Net Force

Unequal (unbalanced) forces produce motion in the direction of the larger force.

Forces in the same direction add together.

What forces can you name? What forces are shown here?

Friction Force opposing motion ALWAYS works in opposite direction of motion –Causes objects to slow down and stop

Types of Friction Types: 1.Static: acts on objects NOT moving Holds objects in place 2.sliding friction: objects slide to produce friction Brakes, basketball shoes 3.rolling friction: objects roll; bicycle or car tires 4.fluid friction: fluids (air, water,etc.) moving over a surface 1.Aerodynamic: shapes that make lower air friction

How much friction? Depends on materials and force between objects –Rough surfaces = more or less friction? –Smooth surfaces = more or less friction? –Heavy objects = more or less friction? –Lighter objects = more or less friction?

Gravity: Tim and Moby explain Tim and Moby explain Force that pulls objects towards each other depends on the mass of and the distance between them –Accelerates objects towards Earth Law of universal gravitation: all objects have a gravitational pull on all other objects Which object has the most gravity? Why? Which object has the least gravitational pull on it? Why?

Weight vs. Mass Mass: amount of matter in an object Weight: measure of force of gravity on an object –It’s a FORCE! –Weight = mass X gravity –The mass does not change but the weight is determined by the force of gravity! –Man on the moonMan on the moon

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