Chapter 10 Forces

(10.1) The Nature of Force GOAL: To understand how force is distributed, and how forces act on one another. VOCABULARY Force Newton Net force Unbalanced Forces Balanced Forces

What is a force? FORCE: A push or a pull of an object on another object. List 5 forces that you encountered today. Similar to velocity and acceleration, a force is described by its strength and by the direction it goes.

Newton NEWTON: The SI unit for force is called the Newton (N). Forces are represented with arrows. A Newton = Kg m/s2

Combining Forces Many forces can be applied on an object at one time. NET FORCE: the combination of all forces acting on an object. Of the 5 examples of forces you drew. Draw a picture with arrows that describes the force.

Unbalanced/Balanced UNBALANCED FORCE: results in a net force that can cause an object to move. BALANCED FORCE: results in a stationary object, all forces are cancelled out.

(10.2) Friction and gravity GOAL: Understand the factors that determine friction, and factors that affect gravity. VOCABULARY Friction weight Static friction free fall Sliding friction air resistance Rolling friction terminal velocity Fluid friction projectile Gravity Mass

Friction Describe all of the friction you see in the picture.

friction Friction: the force between two objects when rubbed against one another. The strength of friction depends on 1. How hard the objects push on one another 2. The type of surfaces involved

Types of frictions Static, sliding, rolling, and fluid. STATIC: friction that acts on objects that aren’t moving SLIDING: friction when an object is sliding over another. ROLLING: friction from an object rolling over another object. FLUID: friction when a solid object flows through a liquid.

gravity GRAVITY: a force that pulls objects toward one another. Mass and distance affect gravity

Weight and mass Weight: the force of gravity on a person Mass: amount of matter a person has

FREE FALL FREE FALL: when the only force acting on a falling object is gravity. AIR RESISTANCE: an upward force on an object falling through the air. TERMINAL VELOCITY: is reached when the force of air resistance equals the force of the weight falling.

(10.3) Newton’s laws GOAL: Be able to recall and understand the differences in Newton’s Laws. VOCABULARY Inertia Momentum Law of conservation of momentum

1st law 1st LAW: an object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force.

INERTIA INERTIA: The tendency of an object to resist a change in motion.

2nd law 2nd LAW: acceleration depends on the object’s mass and on the net force acting on the object. Force=mass x acceleration (1) Calculating Force What is the net force on a 1,000-kg object accelerating at 3 m/s2?(2) Calculating Force What net force is needed to accelerate a 25-kg cart at 14 m/s2?

2nd law In this picture, what do we need to know in order to calculate the net force of the wagon?

3rd law 3rd LAW: if one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object.

momentum MOMENTUM: is a characteristic of a moving object that is related to the mass and the velocity of the object. Momentum= mass x velocity (1) Calculating Momentum A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has greater momentum?

Law of conservation of momentum LAW OF CONSERVATION OF MOMENTUM: The total momentum of any group of objects remains the same, or is conserved, unless outside forces act on the objects.