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

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

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

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.

Balanced forces

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

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.

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.

Add forces acting in the same direction
8 N + 6 N = 14 Newtons

Subtract forces acting in opposite directions
20 N – 18 N = 2 Newtons

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

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

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.

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.

Law of Inertia (1st law)

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.

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.

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.

Therefore Force = Mass X Acceleration Force = 1,000 kg X .05 m/s/s
Force = 50 Newtons

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

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?

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?

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?

Newton’s 3rd Law of Motion
For every action, there is an equal but opposite reaction

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

Newton’s 3rd Law

Space Shuttle Launch

Speed/Velocity How fast an object is moving
Rate at which an object covers a distance Speed = distance/time (meters/second)

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

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

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.

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

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

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

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

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

Moving away at a constant speed
Stopped moving (no motion) Accelerating

Distance Time Graphs

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?

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)

Interpret the graph below

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

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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