Presentation on theme: "CARS and Safety Features Inertia To be able to: AllMostSome Describe what inertia is (MYP 2/3) Explain how inertia works (MYP 3/4) Describe how car manufactures."— Presentation transcript:
Inertia To be able to: AllMostSome Describe what inertia is (MYP 2/3) Explain how inertia works (MYP 3/4) Describe how car manufactures have tried to over come inertia (MYP 6/6) Criteria A,C
Newtons First Law of Motion An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. "the law of inertia". This law is often called "the law of inertia".
Newtons Second Law of Motion Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).
F orce (N) = m ass (kg) x a cceleration (m/s/s) The bigger the force, the …higher/lower…. the acceleration The bigger the mass, the …higher/lower…. the acceleration Newtons Second Law of Motion
Rearrangements of formula mass acceleration m a F a = F m m = F a F = ma m = F a a = F m F = ma 5
How much force is needed to accelerate a 70kg rider and her 200kg motorcycle at 4 m/s/s? m = (200 + 70) kg a = 4 m/s/s F = ? F = m a = 270 x 4 = 1080 N Which equation? 7
Problem Solving 1. A sports car and a furniture van are both travelling at a speed of 60km/h. Which vehicle would require more force to stop it? Explain. 2. What would be the acceleration of 85kg wagon with a force of 382.5N? 3. a) What force is needed to accelerate an empty 1000kg car at 3 m/s/s. b) The same force is then applied to the same car with a student inside. If the resultant acceleration is 2.8m/s/s, what is the mass of the student? 6
1. The furniture van would require more force to stop because its mass is greater 7 ANSWERS
3. What would be the acceleration of 85kg wagon with a force of 382.5N? a = F m = 382.5 85 = 4.5 m/s/s Which equation? 7
4. What force is needed to accelerate an empty 1000 kg car at 3 m/s/s. The same force is then applied to the same car with a student inside. If the resultant acceleration is 2.8m/s/s, what is the mass of the student? F = m a = 1000 x 3 = 3000 N m = F a = 3000 2.8 = 1071.4 kg students mass = (1071.4 – 1000) = 71.4kg
Energy loss in collisions Weve also said that in a collision momentum is conserved (unless an external force acts). The same cannot usually be said for kinetic energy… For example, consider the following collision. How much kinetic energy is lost? Kinetic energy = ½ x mass x velocity squared in J in kg in m/s In the Forces module we looked at how to calculate an objects kinetic energy:
Energy loss in collisions Mass = 1000kg Mass = 800kg Speed = 50m/s Speed = 20m/s Mass = 1000kg Mass = 800kg Speed = 20m/s Speed = 30m/s Before After
Energy loss in collisions Consider a head-on collision where the cars stick together. How much kinetic energy is lost in this example? Where does all the energy go? In this example more kinetic energy was lost. We say it was a less elastic collision. An elastic collision is one where the kinetic energy is conserved. Speed = 50m/sSpeed = 30m/s Speed = 10m/s Before After
Car safety Features To be able to: AllMostSome Describe what features have to improve safety (MYP 2/3) Explain how each feature works (MYP 3/4) Describe how car manufactures have improved safety features over time (MYP 6/6) Criteria A,C
Car Safety Features The greater the speed, the longer it will take to decelerate in a collision, leading to a greater force and greater damage and injury.
Car Safety Features Seatbelts Air bags Head restraints Crumple Zones Collapsible Steering Column Padded dashboards Collapsible bumper bar
Car Features ABS Crumple zones Seatbelt Air bags
Air Bags Airbags are a flexible envelope that is designed to inflate rapidly in the advent of an accident. They are triggered automatically if the car suffers a sudden impact, and once inflated they provide cushioning for occupants. This is meant to limit and even prevent the kinds of major trauma occupants of cars can receive in a crash.
The airbag is connected to a range of sensors in the car which measure things like acceleration, impact, wheel speed etc. When an impact is sensed by these, the airbag is inflated by a gas propellant that inflates a nylon bag. The actual process occurs in a fraction of a second so that a cushion appears in front of or beside an occupant pretty much instantaneously.
Crumple Zones The crumple zone of the automobile is the thing that keeps the passengers safe inside the passenger compartment of the automobile, because around your car, the fenders and certain portions of the car have been designed by automobile manufactures to crumple, to collapse, to absorb the crash forces during the collision. The car won't make out so well, but you'll survive the crash.
Seat Belts The job of the seatbelt is to hold the passenger in place so the passenger is almost part of the car which prevents the passenger from flying forward as the car stops abruptly in the case of a collision. When a car stops suddenly due to a collision with another object the car's acceleration decreases very quickly in a short period of time. deceleration. This is called deceleration.
As the car collides with another object, the other object provides the force which changes the speed and direction. The car stops going in the direction it was going in, and in some cases bounces back depending how hard of a force hits it or how much momentum the car had.
Also, the speed decelerates quickly due to the impact. When all this happens the passenger is not being acted upon by a force to slow them down.
As the person continues in their same direction and speed ( forward and the same speed that the car was going) the seatbelt catches them, holding them back from flying through the air.
The alternative is to not wear a seatbelt, but a force will still have to act on the person in order to slow them down. This force will come from the dashboard or windshield as the person crashes into it causing a lot of damage to themselves.
Hydraulic systems use the principle that pressure is transmitted throughout a liquid. Hydraulics They are used to transfer movement from one part of a machine to another without linking the parts mechanically. All hydraulic systems use two pistons linked via a pipe which carries special oil called hydraulic fluid.
Hydraulics Pressure inside all parts of the hydraulic system is the same Force applied here Force transferred here
All hydraulic brake systems (e.g. in a car) use a small master piston and a bigger slave piston. The master piston is used to apply a force. This puts the liquid under pressure. The pressure is transmitted to the pistons on all four wheels of the car. Hydraulic Brake foot pedal master piston hydraulic fluid slave pistons
The pressure exerted by the master piston on the hydraulic fluid can be calculated using this equation: pressure = force applied area of master piston Hydraulic Brake – Pressure Equations
The slave piston has a larger area than the master piston, so the force exerted by the slave pistons is greater than the force exerted by the driver on the brake pedal. The pressure is transmitted to the slave pistons, so the force exerted by the slave piston can be calculated using: pressure = force exerted area of slave piston force exerted = pressure × area of slave piston
The master piston of a car has an area of 5 cm 2. Hydraulic Brake – calculations 1. If a force of 10 N is applied to the master piston, calculate the pressure created in the brake pipes. 2. If the slave piston (the brake pads) has an area of 50 cm 2, calculate the force exerted on the brake disc. brake pedal axle master piston brake disc slave piston wheel
Hydraulic brake – Answers 2. At the slave piston, f = p × a = 2 N/cm 2 × 50 cm 2 100 N = 100 N So, the force exerted on the brake disc is ten times greater than the original force applied to the master piston. Calculations: 1.At the master piston, p = 10 N 2 N/cm 2 = 2 N/cm 2 Brake pads Brake discs 5 cm 2
ABS- Antilock Brakes Movement of a vehicle when the wheels are locked or stationary is known as skidding and this is what anti lock brakes is supposed to prevent. ABS monitors the rotation of each wheel during braking and any wheel that locks or is about to lock the system reduces the braking force and re-applies it at a rate of several times per second.
ABS- Antilock Brakes Anti lock brakes allows you to steer around obstacles if you can't stop in time as a skidding vehicle can't be properly steered. ABS also allows you to have more control of your vehicle in adverse conditions such as ice, mud and gravel. It also prevents excessive tyre damage as skidding damages your tires and if you apply the brakes hard constantly and skid a lot it can severely reduce the lifespan of your tyres.