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Forces and Motion Demonstrate and calculate how unbalanced forces change the speed or direction of an objects motion

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**Force Any push or pull on an object Act in pairs**

Measured in Newtons (N) Every force has a magnitude and direction Forces can work together or against each other Forces can be balanced or unbalanced

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**Balanced Forces Occurs when there is NO CHANGE in an objects motion**

No acceleration – no change in motion objects are at rest or traveling at a constant speed and direction.

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Balanced forces

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**Unbalanced Forces Always cause a change in motion - Acceleration**

Acceleration – change in speed or direction of an object Starting Stopping Speeding up Slowing down Turning

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**Net Force Combination of all forces acting on an object.**

Add forces working in the same direction. Subtract forces that are working in opposite directions.

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**Vectors Lines with arrows that show force.**

Length of the line shows the amount of force (magnitude) The arrow shows the direction of the force.

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**Add forces acting in the same direction**

8 N + 6 N = 14 Newtons

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**Subtract forces acting in opposite directions**

20 N – 18 N = 2 Newtons

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**Net Force = 0 Forces are balanced**

20 N – 20 N = 0 Newtons Forces are balanced - No change in motion

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**Net force and direction**

What is the net force? What direction are they moving? Why?

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**Newton’s 1st Law of Motion**

Law of Inertia An object at rest will stay at rest unless acted on by an unbalanced force. An object in motion will stay in motion at the same speed and direction unless acted on by an unbalanced force.

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In other words… An object will keep doing what it is doing unless forces become unbalanced Also known as the “Law of Inertia” Inertia – An object’s tendency to resist change in motion.

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Law of Inertia (1st law)

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Vehicle Restraints What is the purpose of vehicle restraints such as seat belts? Describe how Newton’s 1st Law of motion applies to vehicle restraints.

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**Newton’s 2nd Law of Motion**

Law of Acceleration The acceleration of an object by a force in inversely proportional to the mass of the object and directly proportional to the force applied.

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In other words… The smaller the object, the greater the acceleration AND the larger the object, the smaller the acceleration. The smaller the force applied, the smaller the acceleration AND the larger the force applied the larger the acceleration.

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**Therefore Force = Mass X Acceleration Force = 1,000 kg X .05 m/s/s**

Force = 50 Newtons

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Acceleration The rate of change in the velocity, speed and/or direction, of an object. Acceleration = Force/Mass Measured in meters/sec2

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**Force = Mass X Acceleration**

If the amount of force stays the same and the mass of the object increases, what will happen to the amount of acceleration? If the amount of force stays the same and the mass of the object decreases what will happen to the amount of acceleration?

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**What if the acceleration has to stay the same?**

What will have to happen to the amount of force needed if the mass of an object increases? What will happen to the amount of force needed if the mass of an object decreases?

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**Spring Scales Used to measure force.**

Use the spring scale to measure the amount of force needed to pull the CPO car up the ramp with different amounts of weight/mass. What happens to the amount of force when the mass increases?

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**Newton’s 3rd Law of Motion**

For every action, there is an equal but opposite reaction

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**In other words… All forces act in pairs.**

When one object exerts a force on a second object, the second object exerts a force back that is equal in size but opposite in direction

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Newton’s 3rd Law

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Space Shuttle Launch

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**Speed/Velocity How fast an object is moving**

Rate at which an object covers a distance Speed = distance/time (meters/second)

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Calculating Speed While on vacation, Lisa Carr traveled a total distance of 440 miles. Her trip took her 8 hours. What was her average speed? Speed = 440 miles/8 hours Average speed = 55 miles/hour

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**Calculating Distance and Time**

Calculating the amount of time it takes to travel a distance. Time = distance/speed Calculating the distance traveled in a certain amount of time. Distance = speed X time

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**What’s the difference between Speed and Velocity**

Velocity - The rate at which an object changes position. It’s the measurement of the rate and direction of motion.

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**Force = Mass x Acceleration (F = MA)**

Which object would have the greatest force? A 500 g object accelerating at 10m/s2 or A 10 g object accelerating at 10m/s2 Use your formula chart to calculate Force Force = Mass x acceleration

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**Force = Mass x Acceleration**

500g X 10 m/s2 = 5000 Newtons force 10g X 10 m/s2 = 100 Newtons of force The 500g object exerts a greater force

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**What is the motion of the object in the graph below?**

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No motion Moving away fast at a constant speed Stopped (no motion) Moving away more slowly at a constant speed

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**What is the motion of the object in the graph below?**

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**Moving away at a constant speed**

Stopped moving (no motion) Accelerating

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Distance Time Graphs

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**What is the motion of the object in the graph below**

What is the motion of the object in the graph below? What is the speed of the object?

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**Speed = distance ÷ time 5 meters in 1 sec. 25 meters in 5 sec.**

5 ÷ 1 = 5 m/s 25 ÷ 5 = 5 m/s 50 ÷ 10 = 5 m/s This object is travelling at a constant speed of 5 m/s (meters per second)

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**Interpret the graph below**

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**Kinetic vs Potential Energy**

Kinetic Energy – Energy of motion The faster you are travelling the more kinetic energy you have Potential Energy – Stored energy The more stored energy you have built up the more potential energy you have

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**Where does the rollercoaster have the greatest kinetic energy vs**

Where does the rollercoaster have the greatest kinetic energy vs. potential energy

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