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Motion and Forces. Chapter 2. Force. Force- push or pull exerted by one body onto another Not all forces are easily recognized Right now several forces are acting on all of us. Balanced forces. Balanced forces – equal forces act on an object – and cancel each other out
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Motion and Forces Chapter 2
Force • Force- push or pull exerted by one body onto another • Not all forces are easily recognized • Right now several forces are acting on all of us.
Balanced forces • Balanced forces – equal forces act on an object – and cancel each other out • If the upthrust (or push up) of the air is equal to the force of gravity (pull down), then the balloon remains suspended in the air.
Net Force • Net force – when one force is greater then another. This is an unbalanced force- and causes an object to accelerate • There may be many force directions in any one movement
Newton’s first law of motion An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force
Force • Force is equal to the mass of the object times the objects acceleration. If any two of these are known the third can be found. • F = m x a • Mass- kilograms • a = m/s2 • F = Newtons
Inertia • Inertia = the resistance an object has to a change in its state of motion – objects with greater mass have greater inertia
Force is not needed to keep an object in motion. • Forces accelerate or decelerate objects
Friction Friction- force that opposes movement between two surfaces that are touching • Causes of friction – unsmooth surface, deformations, molecular attraction
Question • Imagine a place in the cosmos far from all gravitational and frictional influences. Suppose that you visit that place (just suppose) and throw a rock. The rock will • a. gradually stop. • b. continue in motion in the same direction at constant speed.
Types of Friction • Static friction – force of a resting object • Sliding or Kinetic friction - force on a moving object • Rolling Friction- Friction or a rolling object –similar to kinetic friction