Motion, Forces and Simple Machines Chapter 5

Section 1- Motion

Instantaneous Speed: – The speed of an object at any instant of time is the instantaneous speed! How is instantaneous speed different from average speed? – Instantaneous speed is speed at any instant whereas average speed is speed over a time interval (period of time). Constant Speed: – When the instantaneous speed of an object is the same at any time, the object is going at a constant speed. In other words, the speed is the same throughout time!

Section 2- Newton’s Laws of Motion Force: -A force is a push or pull. -The SI unit used to measure force is the Newton (N) -1 Newton (N) is equal to 1 kg x m/s 2 Force and Acceleration -For an object’s motion to change, a force must be applied to the object -A force can also change an object’s direction. -Gravity is type of force that exist on Earth and always affects objects that are in motion -Anytime an object’s speed, or direction of motion, or both change, a force must have acted on the object

Balanced Forces: – When two or more forces act on an object and their effects cancel out. – They do not cause a change in an object’s motion Unbalanced Forces: – When two or more forces act on an object and their effects DO NOT cancel out. – They cause a change in an object’s motion Net Force: – Net force is the combination of all forces acting on an object When two or more forces act in the same direction on an object, the net force is the sum of the forces When two forces of equal force act on an object, in the opposite direction, they cancel out and we have a net force of 0. When two unequal forces act in opposite direction on an object, you find the net force by calculating difference between the two forces

Newton’s Laws of motion are a set of principles used to explain the motion of objects. Newton’s First Law states that an object in motion will stay in motion, or an object at rest will stay at rest unless an unbalanced force acts on it Friction is a force between two surfaces in contact that resists the motion of the surfaces past each other. Friction always acts in the opposite direction of motion. Inertia is the tendency of an object to resist a change in motion – Relationship between mass and inertia: The more mass an object has, the greater its inertia – Mass measures the quantity of matter

Section 3- Work and Simple Machines Work is done when a force causes an object to move in the same direction as the force that is applied. Work is measured in Joules (J) which is equivalent to (N x m) – For work to be done, you must apply force to an object and the object must move in the same direction as the force you apply. – Work (in J) = force (N) x distance (m) [W = Fd]

The Pulley is an object, like a wheel, that has a groove with a rope or cable running through it. – A pulley changes the direction of the input force to make work easier. – Mechanical advantage of a pulley is 1 – Mechanical advantage of a double pulley is 2 The lever is a rod or plank that pivots around a fixed point called the fulcrum. – 1st class levers: fulcrum is between output force and input force. Used to increase force. – 2 nd class levers: output forces is between input force and fulcrum. Output force is always greater than input force. – 3 rd class levers: input force is between output force and fulcrum. Increases the distance over which the input force is applied.

The wheel and axle is made of two round objects that are attached and rotate together about the same axis. – Calculate Mechanical advantage by dividing the radius of wheel by the radius of the axle. How do the lever, pulley, and wheel and axle make work easier? – A lever increases the input force or the distance over which the force is applied. A pulley changes the direction of the input force and can increase it. A wheel and axle increases the input force and changes its direction.

The inclined plane is a sloped surface, sometimes called a ramp. – it allows you to lift heavy loads by using less force over a greater distance – To calculate mechanical advantage of an inclined plane, you divide the length of the inclined plane by its height The wedge is a moving inclined plane with one or two sloping sides. – It can change the direction of the input force The screw changes the direction of the force you apply