Expedition 3: Fundamental Forces

Forces and Laws of Motion

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Goals

Define force and explain how forces act on matter.

Identify the many forces acting on an object to determine the net force on the object.

Explore the relationship between force, mass, and acceleration.

Apply Newton’s Laws of Motion to understand how forces affect an object’s motion.

Evaluate the impact of forces and motion on society, technological advances, and the exploration of our universe.

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 vector quantity, so it is described by both its magnitude and the direction in 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 forces acting 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 diagram acts as a map of all the forces acting on an object in a given situation

• Vector arrows are 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.

• Inertia is 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.

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.

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• 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 unbalanced force 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 motionless will remain motionless unless an unbalanced force acts on it.

Newton’s First Law

• The Coefficient of friction is the degree of resistance of a surface.

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

• Static friction 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 static friction than kinetic friction.

• Newton’s Second Law of Motion • When a force is 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 relationship between 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 mass of 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 accelerate as they fall. On Earth, the force of gravity causes free-falling objects to accelerate at a constant rate of about 9.8 m/s2. This is known as gravitational acceleration(g).

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Terminal 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. Mass measures 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).

Newton’s Third Law

• Newton’s third Law of Motion states that for every action force, there is an equal and opposite reaction force.

Newton’s Third Law

• When one object exerts a force on a second object, the second object exerts a force equal in size and opposite in direction on the first object.

Newton’s Third Law

• For example when you kick a soccer ball the force exerted on the ball by your foot is called the action force, and the force exerted on your foot by the ball is called the reaction force.

Forces always occur in pairs.

• Action and reaction forces are applied to different objects.

• These forces are equal and opposite.

Forces always occur in pairs.

• Action and reaction force pairs are present even when there is no motion.(EX sitting in a chair)

Forces in a force pair do not act on the same object. .

• Newton’s third law states that forces happen in pairs.

Newton’s Third Law

Newton’s Third Law

Newton’s Third Law

Newtons Third Law

• http://www.youtube.com/watch?v=jO6B0yx3FHE

Terminal Velocity

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Review

• http://www.youtube.com/watch?v=mn34mnnDnKU