Force

1. Force

2. Review • Motion is a change in position • Speed is change in position over time • Velocity is speed plus direction • Acceleration is change is speed or velocity over time a = (vf - vi)/t • +a is speeding up -a is slowing down

3. Force • Newton’s 1st law • An object that is in motion will remain in motion until acted on by an outside force. • What is Force? • A Push or a Pull • Push on your Science Book and it moves along the desk • Push the same amount on a smaller book and it moves faster.

4. Force • Newton’s 2nd law • A force acting on an object will cause that object to accelerate in the direction of the force. • F = m x a • a = F / m • m = F / a • Why don’t things keep going after you apply a force?

5. Force • Friction • Micro welds formed between the microscopic bumps of the surfaces.

6. Force • Friction • Static Friction • The friction between two surfaces that are not moving past each other. • Sliding Friction • The force that opposes motion between two surfaces that are sliding past each other. • Rolling Friction • The frictional force between a rolling object and the surface it rolls on.

7. Force • Air Resistance • Friction that occurs between an object and the medium (air) that it is moving through. • Like other forms of friction it acts in the opposite direction to the motion • Air resistance (amount) depends on the speed, size and shape of the object rather than the mass. • Terminal Velocity – the velocity where the force of air resistance is equal to the force accelerating the object.

8. Force • Gravity • The Law of Gravitation • Anything that has mass is attracted to everything else that has mass. • Gravity is one of the four basic forces in the Universe. • Gravity – Attraction that varies with Mass and Distance • Strong Nuclear and Weak Nuclear – Attraction that acts within the nucleus • Electromagnetic – Electricity, Magnetism & Chemical reactions

9. Force • Gravity • The range of the force of gravity is the universe. • Everything in the universe is attracted to everything else. • The planet Neptune was found because of the affect of its gravity on the orbits of the other planets. • The force of gravity follows the same formula • F=m•a • Near the earths surface a = 9.8 m/s2

10. Force

11. Force • Gravity • Gravitational force on an object is the weight. • Weight is measured in Newtons • An object that masses 100 kg weighs 980 N • Free Fall • Objects that are falling at the rate of gravitational acceleration will appear to float. • Astronauts seem to float because both they and the capsule they are in are falling toward the Earth at the same rate. • At 1000km from the Earth’s surface the force of gravity is only ¾ of what it is at the surface

12. Force • Gravity • In a gravity field all projectiles follow a curved path. • Centripetal Acceleration and Force • Acceleration or force towards the center of the curve. • Projectiles have both horizontal and vertical velocities at the same time. • The Moon is constantly falling toward the Earth. • The Earth is constantly falling toward the Sun.

13. Force • Newton’s 3rd law • For every action there is an equal and opposite reaction • Action and Reaction Forces act on different objects • A swimmer pushes on the water and the water pushes them forward. • Rocket Propulsion • Hot gas is thrown out the back at high speed and the rocket moves in the opposite direction. • Momentum • A property of matter due to its mass and velocity • p = m x v

14. Force • Changing momentum over time is Force • F = (mvf – mvi)/t • Law of Conservation of Momentum • After a collision of a cue ball with the rack on a pool table the total momentum of the pool balls equals the momentum of the cue ball at the moment it hit.