9 Unbalanced forcesUnbalanced forces can change the motion of an object in two ways:When unbalanced forces act on an object at rest, the object will moveWhen unbalanced forces act on a moving object, the velocity of the object will change
10 Work Work: using a force for a distance W = F x d The work done by forces on an object = changes in energy for that object.Work and Energy are measured in Joules1 Joule=1 Newton • meter
11 Use the formula Work = Force x distance 42 How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N?F 300 JG 750 JH 1,000 JJ 15,000 JUse the formula Work = Force x distanceForce of 20 N x 15 meters = 300 Joules Answer:
12 Work: movement of nail is in direction of force EnergyIs defined as the Ability to do WorkSo something has energy if it has the ability to do work.( move an object over a distance in the direction of the force)No work: movement is forward, but force on books is upwardWork: movement of nail is in direction of force
13 distance traveled per unit of time Speeddistance traveled per unit of timespeed = distance / time
14 Calculating Speed Write these in your notebook Speed = Distance Time Speed X TimeWrite these in your notebookTime = DistanceSpeed
15 Which formula?Work with a partner to decide what formula you would use with each of these problems:A car drives 30 miles in 2 hours. Calculate the car's speed.How far would you travel at 80 km / hr for 5 hours?How long would it take to go 250 miles at a speed of 50 miles / hour?Be prepared to share your answers
16 Demonstrate that changes in motion can be graphically represented
17 What does it show?Firstly, look at the axis to see what the graph represents.
18 Drawing graphs of real-life situations In your exams you may be asked to complete, or draw, graphs to represent given situations.
19 Example 1.You are at home getting ready to go out to your stamp collecting club.You leave your house and jog the 1000m to the club. You arrive 5 minutes later.You exchange stamps and chat for 1 hour, then leave for home. It takes you 10 minutes.Plot a distance time-graph to represent your journey to and from the club.
20 Drawing graphs of real-life problems Choose a suitable scale for each axis.2. Decide how many points to plot.You are at home getting ready to go out to your stamp collecting club.You leave your house and jog the 1000m to the club. You arrive 5 minutes later.You exchange stamps and chat for 1 hour, then leave for home. It takes you 10 minutes.You are at home getting ready to go out to your stamp collecting club.You leave your house and jog the 1000m to the club. You arrive 5 minutes later.You exchange stamps and chat for 1 hour, then leave for home. It takes you 10 minutes.3. Draw the graph with suitable accuracy4. Provide a title and label the axisThe journey to and from my stamp collecting club2004006008001000Distance from home (m)Time (minutes)
21 Velocity describes the speed and direction of a moving object
22 airplane moving towards the west with a speed of 482 km/hr Speed or Velocity?Read the following and work with a partner to decide if the following represent “Speed” or “Velocity”airplane moving towards the west with a speed of 482 km/hrcar moving at 80 km/hrBe ready to explain your answers
23 Speeding up and slowing down are changes in speed
24 Change in speed or direction AccelerationChange in speed or directionAn object is accelerating when it speeds up, slows down, or changes direction
25 Acceleration 3 Examples: Case 1 – Interval increases because car is moving faster and fasterCase 2 – Interval decreases because car is slowing downCase 3 – Interval stays the same, but direction of motion is constantly changing
26 Slowing down is sometimes called deceleration AccelerationSlowing down is sometimes called decelerationTPS: work with a partner to explain why coming to a stop at a traffic light is acceleration.Be ready to share your answer
27 Newton’s First Law of Motion Newton’s First Law of Motion states that an object will remain at rest, or move at a constant speed in a straight line, unless it is acted on by an unbalanced force
28 Newton’s First Law of Motion inertia – tendency of an object to stay at rest or in motionNewton’s First Law of Motion is also called the Law of InertiaWatch this animation, then TPS to explain why is it important to wear seatbelts when riding in a car.Be prepared to share your thoughts with the class.
29 Newton’s First Law in action! After watching the film clip, quickly sketch this drawing in your notebook. Add a seatbelt to the driver. Use another arrow to show the force that the seatbelt exerts to prevent the man from flying out of the carNewton’s First Law in action!
30 Now check your sketch by watching this film clip: Car CrashDo you need to make any changes to yoursketch?If so, do it now.Write a paragraph to describe how seatbelts andcar crashes are related to Newton’s First Law of Inertia.
31 Newton’s Second Law of Motion Newton’s Second Law of Motion describes the relationship among force, mass, and accelerationWatch this clip and then TPS to explain what can cause the elephant to move faster.
32 Newton’s Second Law of Motion Unbalanced forces cause objects to accelerateThe amount by which an object accelerates depends on two thingsSize and direction of the forceMass of the object
33 Newton’s Second Law of Motion If two forces act on the same object, the larger force will produce more acceleration than the smaller force
34 Newton’s Second Law of Motion If you apply the same amount of force to two objects with different masses, the object with the smaller mass will accelerate more than the object with the larger mass
35 TPS to discuss: How can you apply a force to two objects with different masses, but still have them accelerate at the same rate?
36 Newton’s Second Law of Motion force = mass X accelerationF = m x aForce is measured in Newtons (N)Newton – unit of force equal to one kilogram-meter per second per second
37 Newton’s Third Law of Motion Newton’s Third Law of Motion states that for every action force, there is an equal and opposite reaction force
38 Newton’s Third Law of Motion Forces always act in pairsThe two forces act in opposite directions
39 Newton’s Third Law of Motion action force – force acting in one directionreaction force – force acting in the opposite direction (scroll down to boat animation)Watch the animation, then TPS to explain why the boat moved away from the dock.
40 Review Match the following to the Newton’s Law that explains the motion in each picture 1St Law ?2nd Law?Or3rd Law?