3 At this moment you are exerting an attractive force on everything around you This force is called gravityAnything with mass is attracted by gravityOne of the four basic forcesElectromagnetic forceStrong nuclear forceWeak nuclear forceGravityWhat is Gravity?
4 GRAVITY is an attractive force between two objects that depends on the masses of objects and the distance between them.Increases with massIncreases as objects move closerOnly Earth is close enough and large enough that you can feel its attractionWhat is Gravity?
5 The Law of Universal Gravitation Scientists wanted to be able to calculate the gravitational force between two objectsIsaac Newton published the Law of Universal Gravitation in 1687.F = G m1 m2 F = gravitational forced2 G = Universal gravitation constantm1 = mass of object 1m2= mass of object 2d = distance between the two objects.The Law of Universal Gravitation
6 The Range of Gravity m2= mass of object 2 Attraction rapidly decreases as two masses move away from each other.How rapidly?Let’s look at the equation…F = G m1 m2 F = gravitational forced2 G = Universal gravitation constantm1 = mass of object 1m2= mass of object 2d2 = distance between the two objects.The Range of Gravity
7 Earth’s Gravitational Acceleration If you dropped a bowling ball and a marble at the same time, which would hit the ground first?What if there were no air resistance?Acceleration due to gravity (g) is 9.8 m/s2Earth’s gravitational force can be calculated:F = mg F= force (N)m= mass (kg)g = gravitational accelerationEarth’s Gravitational Acceleration
8 Gravitational force is acting on you whether you are falling or standing on the ground. Gravitational force acting on an object is weight.W = mg W = weight (N)m = mass (kg)g = gravitational accelerationWeight
9 Weight and Mass Weight and mass are not the same Weight is a forceMass is the amount of matter in an objectWeight can change with gravitational forceMass will not changeWeight and Mass
10 Weightlessness and Freefall Notice that object in space shuttles always seem to be floatingThey aren’t floatingThey are fallingThey are all falling at the same accelerationLet’s consider you on a scale in an elevator:What happens when you go up?What happens when you go down?Weightlessness and Freefall
11 Thrown objects do not always travel in straight lines Anything thrown or shot through the air are called projectiles.Gravity causes projectiles to follow a curved pathProjectile Motion
12 Horizontal and Vertical Motions A thrown object has both a horizontal and vertical velocityThe horizontal velocity (resulting from the applied force by the thrower) will be constant in the forward directionBut an object thrown is being pulled by gravity.The object will have a vertical velocity resulting from earth’s gravitational pullThe ball appears to curveThe two motions are independent of each otherHorizontal and Vertical Motions
13 Horizontal and Vertical Distance If I throw a ball and then drop a ball of the same mass at the same time, which will hit the ground first?They will hit at the same time!!Horizontal and Vertical Distance
14 When an object goes around a curve, it accelerates toward the center of the curve. Acceleration toward the center of a curve is called centripetal accelerationThe net force exerted toward the center of the curve is the centripetal forceCentripetal Force
15 Centripetal Force and Traction When a car rounds a corner, a force must act to keep the car moving in a curved pathThe centripetal force is the friction force (traction) between the tires and the roadThe road is slippery and the force is small, the force may not be large enough to keep the car following the curveCentripetal Force and Traction