Expedition 3: Fundamental Forces

Expedition 3: Fundamental Forces Forces and Laws of Motion

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Goals

Expedition 3: Fundamental Forces • A force is anything, such as a push or pull, that causes a change in the motion of an object.

Expedition 3: Fundamental Forces • Force is a vectorquantity, so it is described by both its magnitude and the directionin which it acts.

Expedition 3: Fundamental Forces • Force is measured in the SI unit: newton.

Expedition 3: Fundamental Forces • Net force is the sum of all forcesacting on an object at any given moment.

Expedition 3: Fundamental Forces • Friction is the force exerted on two touching surfaces, causing a resistance in motion.

Free-body diagram • A free-body diagramacts as a map of all the forces acting on an object in a given situation

Vector arrowsare used to show the magnitude, or strength, and direction of all forces in relation to each other. • http://www.youtube.com/watch?v=hSQM0hoS6VE

Balanced and Unbalanced Forces • Balanced and Unbalanced Forces • When the net force applied an object is not zero, the forces are described as unbalanced.

Inertiais the tendency of an object to resist any change in its motion.

Inertia • All objects resist changes in motion, so all objects have inertia.

Inertia • An object that has a small mass, such as a baseball, can be accelerated by a small force.

Inertia • But accelerating an object whose mass is larger, such as a car, requires a much larger force.

Inertia • Thus, mass is a measure of inertia. • An object whose mass is small has less inertia than an object whose mass is large does.

http://www.youtube.com/watch?v=0acpJty6sZM&feature=related • http://www.youtube.com/watch?v=QbGV6qQcJrw&feature=related

http://www.youtube.com/watch?v=LEsK9u_2RYk • http://www.youtube.com/watch?v=PXoDeyybpx0 • http://www.youtube.com/watch?v=R8BfsRHAc7U • http://www.youtube.com/watch?v=TI00v8TSSbA • http://www.youtube.com/watch?v=7gfWvexu4u4&feature=related

Newton’s First Law • An object that is moving will continue to move with the same velocity, until an unbalancedforce acts on it to stop it, change its speed, or change its direction.

Newton’s First Law

Newton’s First Law • This also means that an object that is motionlesswill remain motionless unless an unbalanced force acts on it.

Newton’s First Law • The Coefficient of frictionis the degree of resistance of a surface.

The largerthe coefficient of friction is between any two objects, the more force is required to move the objects and keep them in motion.

Staticfriction acts on objects that are not moving. Kinetic friction acts on objects that are in motion.

Kinetic (moving) friction can be further broken down into three basic types: sliding, rolling, and fluid.

More force is usually needed to overcome staticfriction than kinetic friction.

Newton’s Second Law of Motion • When a forceis applied to an object, the object will accelerate.

Newton’s Second Law • Newton’s second law: The unbalanced force acting on an object equals the object’s mass times its acceleration.

Newton’s Second Law of Motion • The relationshipbetween force and acceleration is described in the equation: force equals an object’s mass multiplied by its acceleration. • F = m x a

Newton’s Cannon • http://waowen.screaming.net/revision/force&motion/ncananim.htm

F = m x a • Force is measured in newtons. • One newton is the force that gives a mass of one kilogram an acceleration of one meter per second squared: 1 N = 1 kg × 1 m/s2 • The pound (lb) is sometimes used as a unit of force. One newton is equal to 0.225 lb. Conversely, 1 lb equals 4.45 N.

Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's Second Law, you can compute how much force Mike is applying to the car

Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's Second Law, you can compute how much force Mike is applying to the car Answer = 50 newtons

The Force of Gravity • All objects with mass are attracted to each other by a type of force called gravitational- force.

The Force of Gravity • The magnitude of this force depends on the massof the two objects and the distance between them.

Law of Universal Gravitation • When the masses are very large, however, the gravitational force will be strong enough to hold the planets, stars, and galaxies together.

The force of gravity causes objects to accelerateas they fall. On Earth, the force of gravity causes free-falling objects to accelerate at a constant rateof about 9.8 m/s2. This is known as gravitational acceleration(g).

http://www.absorblearning.com/media/attachment.action?quick=54&att=360Terminal velocity • When the only force acting on a falling object is gravity, that object is said to be in freefall.

http://www.youtube.com/watch?v=5C5_dOEyAfk • http://www.youtube.com/watch?v=5N9t5qOSzCU

Weight and Mass • Mass and weight are often confused with each other. Massmeasures the amount of matter in an object. • Weight measures the gravitational force exerted on an object

Weight is measured in newtons. • For example, a 66 kg astronaut weighs 66 kg × 9.8 m/s2 = 650 N (about 150 lb) on Earth. • On the moon’s surface, where g is only 1.6 m/s2, the astronaut would weigh 66 kg × 1.6 m/s2, which equals only 110 N (about 24 lb).

Expedition 3: Fundamental Forces