Motion and Forces Types of Forces 1 2

Motion and Forces

Types of Forces 1. 2. 3. 4. Gravitational Electromagnetic Frictional Strong and Weak Nuclear

Gravitational Forces Force of attraction between all objects as a result of their masses and distances between them. ¡ The higher the masses and the shorter the distances between two objects, the greater the force of gravity. ¡ The smaller the masses and the larger the distances between two objects, the weaker the force of gravity. ¡

Gravity exists between ANY two objects

Why things fall to the ground When we drop an object, the force of gravity is strong because the earth has a large mass and is close by. The object gets pulled to the ground. ¡ Near the Earth’s surface, objects accelerate to the ground at a rate of 9. 8 m/s 2, regardless of their masses. ¡

The gravitational force of the Earth decreases as you move away from the planet. ¡ Different planets and stars will have different forces of gravity at their surfaces due to their different masses. The bigger the object the greater the force of gravity. ¡ Gravitational forces also explain the Earth’s tides ¡

Mass vs. Weight Mass is a measure of the quantity of matter in an object. This does not depend on where the object is. ¡ Weight is a measure of the gravitational force acting on an object. This DOES depend on where the object is. ¡

Weight However, weight and mass are different, how come? weight = Fg = mg which is similar to F=ma m - is mass measured in kilograms (kg) g - gravitational field intensity measured in Newtons/kilogram (N/kg); this is also known as acceleration (m/s 2). Fg - is the force of gravity measured in Newtons (N)

¡ ¡ 1 N = 1 kg x m s 2 We know that earths gravitational pull is 9. 8 N => 9. 8 kg x m = 9. 8 m kg s 2 x kg s 2

Example ¡ What is the gravitational force (weight) of a 60 kg astronaut on the earth’s surface? Intensity of gravitation on earth is 9. 8 N/kg F = mg F = 60 kg X 9. 8 N/kg F = 588 N

Example ¡ What is the gravitational force (weight) of a 60 kg astronaut on the Moon’s surface? F=mg F= 60 kg X 1. 67 N/kg (force of gravity on the Moon) F= 100. 2 N

Gravitational Intensity on the Planets in our Solar System Planet Acceleration (m/s) Intensity (N/kg) Mercury 3. 7 m/s² 3. 7 N/kg Venus 8. 87 m/s 2 8. 87 N/kg Earth 9. 8 m/s 2 9. 8 N/kg Moon 1. 62 m/s 2 1. 62 N/kg Mars 3. 71 m/s 2 3. 71 N/kg Jupiter 24. 79 m/s 2 24. 79 N/kg Saturn 10. 44 m/s 2 10. 44 N/kg Uranus 8. 69 m/s 2 8. 69 N/kg Neptune 11. 15 m/s 2 11. 15 N/kg Pluto . 658 m/s 2 . 658 N/kg

How much do you really weigh? ? ? ¡ Take your weight in kg (pounds/2. 2) and calculate how much weight in Newton’s you are on all the planets in our solar system.

Electromagnetic Force ¡ ¡ ¡ Force of attraction or repulsion between two charged objects or between the poles of two magnets We already discussed this earlier in the year Likes repel, opposites attract

Frictional Force The force that prevents two objects from slipping over each other ¡ Air resistance is also a force of friction ¡ Friction depends on: ¡ l l The smoothness of the surfaces (the rougher the surfaces the greater the friction) The pressure between the surfaces (the greater the pressure the greater the friction)

Friction

Strong and Weak Nuclear Forces Act within the nucleus of an atom ¡ Short range forces ¡ Holds the nucleus together ¡

Hippo & Ping Pong Ball In a vacuum, all bodies fall at the same rate. If a hippo and a ping pong ball were dropped from a helicopter in a vacuum (assuming the copter could fly without air), they’d land at the same time. When there’s no air resistance, size and shape don’t matter!

Video of a Vacuum and two objects https: //www. youtube. com/watch? v =8 RKAb 5 acc. C 0 ¡ Question why do both objects fall at the same acceleration? ¡

Table of Equations from this unit Kinetic Energy Speed of an Object KE = ½mv 2 d=vt Acceleration a = change velocity change of time a=∆v ∆t Force Weight F=ma Fg = mg

Measurement Definition Unit Symbol Kinetic Energy Amount of energy needed to move an object Joules J Mass How heavy an object is in kilograms Kilograms kg Velocity How fast an object is moving in meters/second m/s Distance The distance from one point to another point meters m Time Amount of time measured in seconds s Acceleration The rate of change of velocity per second meters/second 2 m/s 2 Force The amount of effort required to Newton move an object N Force of Gravity The amount of gravitation pull on an object. Newton N Gravitational Pull Newton/kilogram N/kg The intensity of gravity measured in N/kg