Presentation on theme: "Chapter: Forces and Changes in Motion"— Presentation transcript:
1Chapter: Forces and Changes in Motion Table of ContentsChapter: Forces and Changesin MotionSection 1: MotionSection 2: Forces and MotionSection 3: The Laws of Motion
2Forces and Motion2ForceA force is a push or a pull that one object exerts on another object.Objects like floors, chairs, and Earth also exert forces on other objects, including people.
3Force Has Direction and Size Forces and Motion2Force Has Direction and SizeJust like velocity and acceleration, a force has both size and direction.The direction of a force is the direction of the push or pull.Pushing or pulling harder increases the size of the force you exert. The size of a force is measured in newtons (N).
4Forces and Motion2How Forces CombineWhen more than one force acts on an object, the forces combine.The combination of all the forces acting on an object is the net force.
5Combining Forces in the Same Direction Forces and Motion2Combining Forces in the Same DirectionWhen two forces act in the same direction on an object, like a box, the net force is equal to the sum of the two forces.
6Combining Forces in Opposite Directions Forces and Motion2Combining Forces in Opposite DirectionsIf two forces of equal strength act on the box in opposite directions, the forces will cancel, resulting in a net force of zero.
7Combining Forces in Opposite Directions Forces and Motion2Combining Forces in Opposite DirectionsWhen two unequal forces act in opposite directions on the box, the net force is the difference of the two forces.
8Balanced and Unbalanced Forces Forces and Motion2Balanced and Unbalanced ForcesWhen the net force on an object is zero, the motion of the object doesn’t change.The forces acting on an object are balanced forces if the net force is zero.The forces acting on an object are unbalanced forces if the net force is not zero.
9Contact and Non-contact Forces Forces and Motion2Contact and Non-contact ForcesA force is exerted when one object pushes or pulls on another.A force that is exerted only when two objects are touching is a contact force.Non-contact forces are forces that can be exerted by one object on another even when the objects aren’t touching.
10Forces and Motion2GravityGravity is a non-contact force that every object exerts on every other object due to their masses.The gravitational force between two objects is an attractive force that tends to pull the two objects closer together.
11Forces and Motion2GravityThe size of the gravitational force between two objects depends on the masses of the objects and the distance between them.The gravitational force between two objects increases if the mass of one or both of the objects increases.If two objects move closer together, the gravitational force between them increases.
12Forces and Motion2Mass and WeightBecause weight is a force, it is measured in newtons.Weight is not the same as mass. Mass is the amount of matter an object contains, and is measured in kilograms.
13Forces and Motion2FrictionFriction is a contact force that resists the sliding motion of two surfaces that are touching.Friction causes a sliding object to slow down and stop.Friction also can prevent surfaces from sliding past each other.
14Forces and Motion2Static FrictionStatic friction is the force between two surfaces in contact that keeps them from sliding when a force is applied.
15Forces and Motion2Sliding FrictionSliding friction is the force that opposes the motion of twosliding surfaces in contact.Sliding friction exists between all sliding surfaces that are touching.
16Forces and Motion2What causes friction?When two surfaces are in contact, the surfaces stick to each other where the dips and bumps on one surface touch the dips and bumps on the other surface.Friction is caused by the sticking of the two surfaces at these bumps and dips.
17Forces and Motion2The Buoyant ForceThe buoyant force is a force exerted by a fluid on an object that is in the fluid.The buoyant force is always upward.If you are floating in water, the buoyant force is large enough to balance your weight.
18Forces and Motion2Air ResistanceAir resistance is a contact force that opposes the motion of objects moving in air.Just like friction, air resistance acts in the direction opposite to an object’s motion.Air resistance is less for a narrow, pointed object than for a wide, flat object.
19Question 1 Answer 2 A force is a _______ or a _______. Section Check2Question 1A force is a _______ or a _______.AnswerForce is a push or a pull.FL: SC.C.2.3.2
20Section Check2Question 2A force exerted between two objects that are not touching is known as _______.AnswerThe answer is a long-range force. Gravity is a long-range force; although we are not touching the Sun, our planet is being acted on by the Sun to keep it in orbit.FL: SC.C.2.3.1
21Section Check2Question 3You try to push a desk across the floor one direction but a friend is trying to push it the opposite direction. As a result, the desk doesn’t move. This is an example of what kind of forces?A. balanced forcesB. continuing forcesC. extended forcesD. unbalanced forcesFL: SC.C.2.3.6
22Section Check2AnswerThe answer is A. When forces are balanced, the net force is zero.FL: SC.C.2.3.6