1. FORCE and MOTION REVIEW
There will be a quiz at the end of this lecture!!!

2. Measuring Motion
Motion is an object’s change in position relative to a reference point.
Speed is the distance traveled divided by the time interval meters/second etc….
Velocity is the speed of an object in a particular direction meters/second south etc…
Acceleration is the rate at which velocity changes over time. An object accelerates if its speed, direction, or both change meters/second2 etc…

3. FORCE In science, a Force is simply a push or a pull.
Forces have a size and direction.
Forces can change the acceleration of an object which can change the speed or direction of an object.
Force is measured in the SI unit called Newtons (N) or kg X m/s2.
Remember that Weight can also be measured in N because Weight is a measure of the gravitational force on an object and depends upon your location in the universe.
Mass is simply mass and doesn’t change no matter an objects location.
NET Force is the combination of all of the forces acting on an object.
You can have forces that add to each other (act in the same direction) or forces that oppose each other (act in opposite directions).

4. FORCE cont…. Friction is a force that opposes motion.
Static Friction occurs when a Force applied to an object is less than the friction force. In other words, the object does not move.
Kinetic Friction occurs when the Force applied to an object is greater than the friction force. In other words, the forces are unbalanced and the object moves.

5. FORCE cont….
Unbalanced Forces occur when the Net Force is > O in a particular direction.
Balanced Forces occur when the Net Force is = to O. So, there is no movement and the object is at rest.

6. FORCE cont….
Gravity is a universal force acting between any two objects and depends upon the mass and distance between the two objects.

7. Universal Law of Gravitation

8. Gravity and Motion
Objects will fall at the same rate because the acceleration due to gravity is the same for all objects.
Terminal Velocity is the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite to the force of gravity.
Free Fall is the motion of a object when only the force of gravity is acting on it. Remember that gravitational force depends upon mass and distance between objects. So when astronauts are orbiting the earth (i.e. there is not an atmosphere), there is still a gravitational force acting on them. However, there is little or no air resistance.

9. Gravity and Motion cont…..
Orbiting is when an object is traveling around another object in space. When a spacecraft orbits the Earth, it is also moving forward (usually at a very high speed to equal or overcome the gravitational force of the earth). If the space ship wasn’t moving forward, it would fall directly towards the earth.
Projectile Motion is the curved path that an object follows when thrown, launched, or projected near the surface of the earth.

10. Newton’s Three Laws of Motion

11. Newton’s 1st Law
An object at rest remains at rest, and an object in motion tends to stay in motion at a constant speed in a straight line unless acted on by another force.
This Law is often called the Law of Inertia.

12. Inertia
Inertia is the tendency of all objects to resist any change in motion.
An example of this is if your car comes to a sudden stop.
Your body (or mass) wants to keep going at the same velocity. Remember that velocity is speed in a particular direction.
So PLEASE wear a seatbelt !

13. Newton’s 2nd Law of Motion
The acceleration of an object depends on the mass of an object and the amount of force applied.
The larger the object the more force must be applied to accelerate it.

14. Newton’s 3rd Law of Motion
Whenever one object exerts a force on a second object, the seond object exerts an equal and opposite force on the first.
All forces act in pairs. If a force is exerted, another force occurs that is equal in size and opposite in direction.
Action and Reaction Forces.

15. Important Equations Force = mass X acceleration (F = ma)
NET Force is the sum of forces in a particular direction. If the force is opposite, the Forces are subtracted. If the forces are in the same direction, the are added.
Momentum = mass X velocity (p = mv)
Objects with more mass take more ‘Reaction’ force to stop and vice versa Objects with less mass take less ‘Reaction’ force to stop if they were traveling at the same velocity.