# P2.1 Force

## Presentation on theme: "P2.1 Force"— Presentation transcript:

Forces can cause changes to the shape or motion of an object. Objects can move in a straight line at a constant speed. They can also change their speed and/or direction (accelerate or decelerate). Graphs can help us to describe the movement of an object. These may be distance–time graphs or velocity–time graphs. Candidates should use their skills, knowledge and understanding to: interpret data from tables and graphs relating to speed, velocity and acceleration evaluate the effects of alcohol and drugs on stopping distances evaluate how the shape and power of a vehicle can be altered to increase the vehicle’s top speed draw and interpret velocity–time graphs for objects that reach terminal velocity, including a consideration of the forces acting on the object Overview

P2.1.1 Force - Objectives Find out what happens when two objects interact Investigate the ‘resultant’ force on an object State what happens when a resultant force acts on an object

This is an objectThis is the force

This is an objectThis is the force

Weight Lift Drag Thrust

Weight Lift DragThrust

3N5N 2N 96N 0N 3N8N5N 3N 4N 5N EXTENSION 2 1 3 4

If the resultant force acting on a stationary object is: Zero The object will remain stationary Not zeroThe object will accelerate in the direction of the resultant force.

If the resultant force acting on a moving object is: Zero The object will continue to move at the same speed and in the same direction Not zeroThe object will accelerate in the direction of the resultant force.

Weight Reaction

Weight Reaction DragThrust

P2.1.2 Force and Motion - Objectives State what happens when a resultant force acts on an object Investigate what affects the acceleration of an object Use F = m x a in calculations

3N8N 5N The object will accelerate in the direction of the resultant force. Resultant Force = Mass x Acceleration Resultant Force = [N] [kg] [m/s 2 ]

Q1. The vehicle has a mass of 1200kg. The engine is applying a forward force of 500N and the friction from the road is a force of 70N. a) What is the acceleration of the vehicle? (show your working)

P2.1.2 Force and Motion - Objectives Read a velocity-time graph Use a graph to perform calculations Recognise the difference between speed and velocity Calculate the acceleration of an object

P2.1.2 Force and Motion 1.Finish your table, calculating the speed (velocity) of the paper. 2.Plot a graph on A4 graph paper: – Velocity (in m/s) on vertical (y) axis – Time (in s) on horizontal (x) axis 3.What does this graph show? This is not an easy task – do not be afraid of getting it wrong

Velocity-time graph A mountain biker accelerates uniformly down a ramp taking 10s to reach 20m/s. They stay at 20m/s for the next 30s of the course. They then take 5s to slow down to 10m/s as they enter the technical, steep part of the track. They stay at 10m/s for the next 20 seconds. Breaking out of the woods they accelerate to 30m/s in 5s as they hit the high speed part of the course. They maintain 30m/s for the next 20s. They cross the finish line and it takes them 5s to come to a stop. http://www.youtube.com/watch?v=LSqj8c8LaBQ&feature=related

Time (s) Start velocity (m/s) Final velocity (m/s) Change in Velocity (m/s) Acceleration (m/s 2 ) Distance Travelled (m) 0-10020 2

Time (s) Start velocity (m/s) Final velocity (m/s) Change in Velocity (m/s) Acceleration (m/s 2 ) Distance Travelled (m) 0-10020 2100 10-4020 00600 40-452010-10-275 45-6510 00200 65-701030204100 70-9030 00600 90-95300-30-675

Time (s) Start velocity (m/s) Final velocity (m/s) Change in Velocity (m/s) Acceleration (m/s 2 ) Distance Travelled (m) 0-10020 2 10-4020 00 40-452010-10-2 45-6510 00 65-701030204 70-9030 00 90-95300-30-6

Answer all Summary Questions in Textbook: Pages 109, 111 and 113 Complete ‘Speed and acceleration 2’ worksheet Sort out your book Stick in sheets Complete unfinished work Past exam questions: 1, 2 and 3 on page 117 All these tasks need to be completed at some point

Stopping Distance = Thinking Distance + Braking Distance Drinking Drugs Tiredness Distractions Icy road Wet road Poor brakes Worn tyres

Stopping Distance = Thinking Distance + Braking Distance Speed

Stopping Distance = Thinking Distance + Braking Distance Speed

When the brakes of a vehicle are applied, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increase. P2.1.3 Forces and Braking Kinetic Energy Heat Energy

Weight P2.1.4 Forces and Terminal Velocity When a parachutist first jumps out of the plane

Weight P2.1.4 Forces and Terminal Velocity Drag When they reach terminal velocity

Weight P2.1.4 Forces and Terminal Velocity Drag When they open their parachute

Weight P2.1.4 Forces and Terminal Velocity Drag When they descend at a lower terminal velocity

Weight P2.1.4 Forces and Terminal Velocity Reaction When they land on the ground

v-t graph for terminal velocity Time / seconds Velocity / m/s

P2.1.5 Force and Elasticity - Objectives Realise what happens when a force acts on an object Reason why objects stretch and store energy Relate stored energy to the work done Investigate how the extension is related to the force applied

Mass / kgWeight / NTotal Length / m Extension / m 000 0.11 0.22 0.3 0.4 0.5 Results table

Force-extension graph Spring Force / N Extension / m Elastic Band