Force, Motion and Energy

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 Net Force: 14 Newtons (8+6=14) Direction of Force: Right

Subtract forces acting in opposite directions Net Force: 2 Newtons (20-18=2) Direction of Force: Left

Net Force = 0 Forces are balanced Net Force = 0 Newtons (20-20=0) Forces are balanced - No change in motion

Net force and direction What is the net force? What is the direction of the force? Why?

Newton’s Law of Inertia Newton’s 1st Law of Motion An object at rest will stay at rest unless acted on by an unbalanced force. And An object in motion will stay in motion at the same speed and direction unless acted on by an unbalanced force.

What does this mean? Because of inertia, an object will keep doing what it is doing unless forces become unbalanced. Inertia is an object’s tendency to resist change in motion

The car stops but the man keeps going because of inertia Law of Inertia (1st law) The car stops but the man keeps going because of inertia

Vehicle Restraints Describe how Newton’s 1st Law of motion applies to vehicle restraints. Vehicle restraints, such as seat belts, are the unbalanced force that stops you when a car stops suddenly so that you don’t go flying forward. This applies to all vehicle restraints.

Newton’s Law of Acceleration Newton’s 2nd Law The acceleration of an object by a force proportional to the mass of the object and directly proportional to the force applied.

What does this mean? The acceleration of an object depends on the mass of the object and the amount of force applied to the object. Acceleration is any change in motion!!! Starting, Stopping, Speeding up, Slowing down, and changing directions (turning)

In other words… The less massive an object the greater the acceleration The more massive an object the smaller the acceleration. The less force applied the smaller the acceleration The more force applied the greater the acceleration.

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

Practice Calculating Force Which object would exert the greatest amount of 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

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

Acceleration The rate of change in the motion of an object. includes the velocity, speed and/or direction of an object. Stopping, starting, speeding up, slowing down and changing directions How to calculate Acceleration Acceleration = Force/Mass Measured in meters/sec2

Answer the following Questions If the mass of an object increases and the force stays the same, what will happen to the amount of acceleration? Acceleration will Decrease If the mass of the object decreases and force stays the same, what will happen to the amount of acceleration? Acceleration will Increase

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? It would have to INCREASE What will happen to the amount of force needed if the mass of an object decreases? It would have to DECREASE

Newton’s Law of Action/Reaction Newton’s 3rd Law of Motion For every action, there is an equal and opposite reaction

What does this mean? All forces act in pairs. An Action force causes a Reaction force that is equal in size and opposite in direction.

Rocket Launches and Newton’s Law of Action/Reaction A rocket taking off creates an action force of gasses pushing down that causes the reaction force of the rocket going up.

Speed The rate at which an object covers a distance (how fast an object moves) Calculating Speed Speed = distance/time

Practice 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

Velocity Velocity tells an objects SPEED and DIRECTION!!! It includes the direction an object is moving as well as the distance traveled in a given time (speed)

Calculating WORK Work is equal to the amount of force it takes for an object to move a distance. Formula: Work = Force X Distance Work is measure in Joules (Newton/meters)

Practice Calculating WORK How much work does it take to move a box with 50 Newtons of force 10 meters? Work = Force X Distance 50 X 10 = 500 Joules Answer - 500 Joules

Range Range is the difference between the highest and lowest values in a set of data. Calculate the range of the following test scores 89, 73, 84, 91, 87, 77, 94 Subtract the lowest score from the highest 94 – 73 = 21 The range of these test scores is 21 points

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?

Where does the roller coaster have the greatest potential energy?