Presentation on theme: "What is a force? A force is a push or pull, or an action that has the ability to change motion. Forces can increase or decrease the speed of a moving."— Presentation transcript:
2 What is a force?A force is a push or pull, or an action that has the ability to change motion.Forces can increase or decrease the speed of a moving object.Forces can also change the direction in which an object is moving.
3 5.1 How are forces created? Forces are created in many ways. For example, your muscles create force when you swing a baseball bat.
4 Contact-actual touching 2. Long-Range— forces acting at a distance Two Kinds of ForcesFrictional ForceTensional ForceNormal ForceAir Resistance ForceApplied ForceSpring ForceContact-actual touching2. Long-Range— forces acting at a distanceA GravitationalB. ElectromagneticC. Nuclear
5 5.1 How forces act One way forces act is the result of direct contact. A contact force is transmitted by matter directly touching other matter such as wind acting to slow a parachute.
6 5.1 How forces actThe force of gravity between Earth and Moon appears to be what people once called “action-at-a-distance”.Today we know that the gravitational force is carried from the Earth to the Moon by a force field.
7 Four Elemental ForcesAll forces in the universe come from only four basic forces.Electromagnetic forces are important to technology.Gravity is a universal force.
8 Classify these forces as contact forces or the result of force fields.
9 Effects of Forces Forces can cause objects to Change speed Change velocityChange shape
10 Measuring Forces To measure a force, we can use Spring scales Force gauges
11 What are the units for FORCE? Newtons-abbreviated (N)-metric unit for forcePounds-abbreviated (lb)-English unit for force
12 5.1 Units of forceThe pound is a unit of force commonly used in the United States.For smaller amounts, pounds are divided into ounces (oz.).There are 16 ounces in 1 pound.
13 5.1 NewtonsAlthough we use pounds all the time in our everyday life, scientists prefer to measure forces in newtons.The newton (N) is a metric unit of force.
14 5.1 Unit conversionsThe newton (N) is a smaller unit of force than the pound (lb).If one pound of force equals newtons, then a 100 lb person weighs newtons.
15 5.1 Contact forces from ropes and springs Ropes and springs are often used to make and apply forces.Ropes are used to transfer forces or change their direction.The pulling force carried by a rope is called tension.Tension always acts along the direction of the rope.
17 5.1 Spring forcesThe force created by a spring is proportional to the ratio of the extended or compressed length divided by the original (resting) length.If you stretch a spring twice as much, it makes a force that is twice as strong.
18 Vectors (Representing forces) Vectors or scalars are used to represent quantities in physics. We will use vectors to represent forces.A scalar is a line segment, whose length represents only magnitude (amount)A vector is an “arrow” whose length represents magnitude and the direction it points represents the direction the force acts.
19 5.1 The force vectorThe direction of a force makes a big difference in what the force does.That means force is a vector, like velocity or position.Arrows are often used to show the direction of forces in diagrams.
20 Drawing Vectors Length represents magnitude, or amount Direction is direction of forceDraw a vector representing a force of 25 Newtons acting to the right.
21 5.1 Drawing a force vectorThe arrow points in the direction of the force.
22 Drawing Vectors Length represents magnitude, or amount Direction is direction of forceDraw a vector representing a force of 25 Newtons acting to the right.Draw a vector representing a force of 50 N acting to the left
23 Resultant ForceSometimes, forces act together. When they do, it is as if they were equal to just one forceA NET FORCE is the force that results from the addition of two or more forces.VAVBVR
24 Tip to Tail Method20 NPlace the tail of one vector at the tip of the other.The vector sum (also called the resultant) is shown in red. Draw resultant vectors from beginning (tail) first vector to end (tip) of last vector.The resultant is also called the “NET FORCE”16 N20 N16 N4 N21 N12 N9 N9 N12 N
25 Draw the Vectors…..Two workers are moving a refrigerator. One pushes forward with a force of 200 newtons, the other pushes forward with a force of 300 newtons.. The net force they (together) exert on the refrigerator is:?
26 Draw the Vectors…..Two students are moving a refrigerator. One pushes forward with a force of 200 newtons, the other pushes backward with a force of 300 newtons. Force is a vector. The total force they (together) exert on the refrigerator is:
27 Forces in CombinationForces acting in same direction are added together to find “Net Force”Forces acting in opposite directions are subtracted to find “Net Force”
36 Gravitational Force The attractive force acting between all masses This is a major force but it is the weakest of all the long range forces!
37 Factors effecting the Stength of a gravitational attraction Masses of two massesDistance between the two massesLarger masses = greater attractionLarger distances between masses = less attraction
38 5.1 GravityThe force of gravity on an object is called weight.At Earth’s surface, gravity exerts a force of 9.8 N on every kilogram of mass.
39 5.1 Weight vs. mass Weight and mass are not the same. Mass is a fundamental property of matter measured in kilograms (kg).Weight is a force measured in newtons (N).Weight depends on mass and gravity.
40 Weight depends on mass and gravity A 10-kilogram rock has the same mass no matter where it is in the universe. On Earth, the10 kg. rock weighs 98 N.. On the moon, the same rock only weighs 16 N.
42 Sig. fig. = 600 N Sig. fig. = 200 N Solving Problems Calculate the weight of a 60-kilogram person (in newtons) on Earth and on Mars.Looking for:…weight of person in newtons on both planetsGiven:…mass = 60 kg; g = 3.7 N/kg on Mars;…implied g = 9.8 N/kg on EarthRelationships:W = m x gSolution:60 kg x 9.8 N/kg = 588 N60 kg x 3.7 N/kg = 222 NSig. fig. = 600 NSig. fig. = 200 N
43 Would you weigh more or less on a mountain compared to a plain?
44 Ocean TidesThe Moon is primarily responsible for ocean tides on Earth.The Sun contributes to tides also.What are spring tides and neap tides?