2What is force?A force is a push or a pull one body exerts on another body.Sometimes it is obvious a force has been applied, but other forces are not as noticeable.Forces can cause a change in motion.
3Balanced forcesWhen two or more forces act on an object at the same time, the forces combine to form the net force.Forces on an object that are equal in size and opposite in direction are called balanced forces.
4BALANCED FORCESBalanced forces do not cause acceleration. (any change in speed or direction)
5Unbalanced forces Unbalanced forces cause a change in motion. Unbalanced forces cause an object to start moving, stop moving, or change direction. (an unbalanced force will cause an object to accelerate)
6Unbalanced forcesThe forces acting on an object may not always be opposite in direction.The net force that acts on this box is found by adding the two forces together.
7Force Diagrams In what direction and with how much force would the object travel?
8Types of Forces A force can be either balanced or unbalanced. Common types of force include gravity, magnetism, friction, air resistance, or centripetal force
9Friction Suppose you give a skateboard a push with your hand. According to Newton’s 1st law of motion, if the net force acting on an object is zero, it will continue to move in a straight line with constant speed.Does the skateboard keep moving forward with a constant speed after it leaves you hand?
10Friction Recall that when an object slows down it is accelerating. By Newton’s 2nd law of motion, if the skateboard is accelerating, there must be a net force acting on it.The force that stops the skateboard is friction.
11FrictionFriction is the force that opposes motion between two surfaces that are touching each other.The amount of friction depends on;1: kinds of surfaces2: the force pressing the surfaces together
12Types of FRICTION Sliding friction- dry solid surfaces Rolling friction- rolling over a surfaceFluid friction- object moves through a liquid or gas.
13Gravity Gravity’s attractive force depends on 1. the distance between the two objects2. the mass of the two objectEvery object exerts a gravitational force on every other object
14GravityIsaac Newton formulated the law of universal gravitation, which he published in 1687.His law states that gravitational force=(constant) x (mass 1)x(mass 2) = G m1m2(distance) d2According to the law of universal gravitation, the gravitational force between two masses decreases rapidly as the distance between the masses increases.
15GRAVITYFree fall- when the only force acting on a falling object is gravity. (9.8m/s/s)Do all objects regardless of mass fall at this rate?What about projectiles?
17GRAVITYAir resistance- a type of fluid friction that objects falling through air experience.Paper vs.. BookWeight- The measure of the force of gravity on an object (scale)Mass- is a measure of the amount of matter in that object.
18Weight Weight and mass are NOT the same. Weight is a force and mass is a measure of the amount of matter an object contains.Weight and mass are related. Weight increases as mass increases.
19Weight on different planets The weight of an object usually is the gravitational force between the object and Earth.The weight of an object can change, depending on the gravitational force on the object.
20Air resistanceWhen an object falls towards Earth, it is pulled downward by a force called gravity.However, a friction-like force called air resistance opposes the motion of objects that move through air.Air resistance causes objects to fall with different accelerations and different speeds.
21Air resistanceThe amount of air resistance on an object depends on the speed, size, and shape of the object.Air resistance, not the objects mass, is the reason feathers and leaves fall slower then pennies or apples.
22What about circular motion??? Bucket DemonstrationWhat is the centripetal force for a satellite?Centripetal- “center seeking”Centripetal force- any force that causes an object to move in a circle.