Forces and Motion

What is a force? A push or a pull Force is something that causes a body to move, change its speed or direction, or distort (change) its shape Forces can be balanced causing no change in motion (meaning to continue at the same speed or to stay motionless) Unbalanced forces cause a change in motion due to one force being greater than the other

What is motion? Motion is a change in position of an object compared to a reference point Reference points are usually stationary objects on Earth like a tree or building Forces cause motion

More on Motion Speed is the rate an object moves and is calculated as S = D/T where d=distance and t=time Velocity is an object’s speed with direction ex: The car was traveling 85km/h to the south Acceleration is the change in velocity of an object, it can be positive (increasing acceleration) or negative when slowing down (deceleration) Momentum is an object’s mass x it’s velocity (M=mv)

Gravity (non-contact) Friction (contact) Magnetism (non-contact) Some Types of Forces Gravity (non-contact) Friction (contact) Magnetism (non-contact) Elastic (contact) Static Electricity (non-contact)

Gravity Gravity – A non-contact force of attraction between two objects. Objects have an attraction to each other. The more mass an object has, the more gravity. That’s why everything falls back to our massive planet! Newton’s Law of Gravitation The gravitational attraction between two objects is dependent on the mass of the two objects and the distance between them.

More Gravity How do the gravitational forces affect objects? Acceleration – all objects accelerate at a constant speed of 9.81 M/S2 When all other forces are equal, different objects dropped from the same height will accelerate at the same rate The more mass, the greater the force an object has Weight, it is the gravitational pull on the object’s mass Mass is the amount of matter in an object regardless of the gravitational pull Projectiles fall in a curved path known as a trajectory

Friction A contact force that opposes motion Results when two objects rub against each other Friction can be useful as in a car race Friction can be harmful if you are trying to skate or ski Rough surfaces increase friction Smooth surfaces decrease friction

Magnetism Magnetism is a non-contact force. A magnetic field is shown left; notice the bands of force as they move around a magnet. Also, notice the bands of force between two magnets.

What Is Energy? Kinetic Energy – The energy of motion. The more energy an object has, the more force it has. Potential Energy – The kinetic energy an object potentially has. It is also known as stored energy.

Newton’s Three Laws of Motion Written in 1687 Describe the motion we observe Explain the forces behind the motion 1st Law = Inertia 2nd Law = F=MA 3rd Law = Action/Reaction

Inertia – The First Law Newton’s First Law of Motion It states that objects at rest stay at rest, and objects in motion stay in motion until a force acts upon them. Inertia is why seat belts are so important to wear! It is also why you can pull the rug out from under something.

Force = Mass x Acceleration - The Second Law Newton’s Second Law of Motion It states that if you increase the force, then the acceleration increases, or if you increase the acceleration, then the force increases. A little bit of algebra! You can also change the mass to affect the force.

Action/Reaction – The Third Law This is Newton’s Third Law of Motion It states that for every action, there is an equal and opposite reaction This is why a rocket pushes up as the engines push down