Forces and motion Flashcards
(20 cards)
What is the speed for walking, running and biking?
Walking - 1.5 m/s
Running - 3 m/s
Biking - 6 m/s
What is the speed of sound?
The speed of sound is 330 m/s
What is acceleration?
Acceleration is the rate at which velocity changes it is measured in m/s^2
What does a distance time graph tell us?
A straight line tells us that the object is going at a constant speed. The speed is the gradient - the steeper the line the higher the speed.
How do you find the speed of an object in non-uniform motion at one point?
You draw a tangent at the point you want to find the speed and you measure the gradient of that tangent which is the speed.
How do you find the distance in a speed time graph?
You find the area under the line on a speed time graph, if the line isn’t straight you can count squares to find the area.
What is Newton’s first law?
Newton’s first law tell us that if there is no resultant force an object will remain stationary or stay at a constant speed.
What is Newton’s second law?
An object’s acceleration is directly proportional to the resultant force acting on it and inversely proportional to the mass.
What is inertial mass?
Inertial mass is a measure of how difficult it is to change an object’s velocity.
How can Newton’s second law be verified by an experiment?
The ramp needs compensating for friction by tilting slightly so that the trolley travels at a steady speed when
pushed.
The equipment above can be used to measure the acceleration for objects when the mass is changed and the
accelerating force is kept constant.
It can also be used to measure the acceleration when the accelerating force is changed and the mass is kept
constant (in order to do this the weights should be taken from the weight stack and added to the trolley –
otherwise the mass of the system will change)
What happens to the forces and acceleration of a falling object?
An object falling due to only gravity is said to be in freefall. This object will accelerate at 9.8m/s^2. In reality the object will experience air resistance and so the resultant force will decrease until the downward force of the weight is equal to the force of air resistance meaning the object is at a constant velocity. This is called terminal velocity.
What is stopping distance?
Stopping distance is the total distance required for a moving vehicle to stop. The equation is:
Thinking distance + Stopping distance.
What is thinking distance?
Thinking distance is the time it takes for someone to react to a hazard and press the brakes.
What is stopping distance?
Stopping distance the distance taken for the car to come to a stop after the brake is pressed.
What factors affect thinking distance?
Speed (car travels further), if the driver is intoxicated (slower reaction time), how tired the driver is (slower reaction time) and whether there are any distractions present (slower reaction time).
What factors affect braking distance?
Speed (takes longer to slow down), Conditions of road (e.g ice or gritty will take longer to stop on) and Condition of the tires/brakes (might apply less friction so stops slower).
What energy transfers occur during braking?
The brakes do mechanical work by applying a force to transfer energy from the kinetic store of the car to the thermal energy store of the brakes. If this transfer happens to quickly, the brakes can overheat and fail causing the car to skid.
Why do we stop vehicles gradually?
If we stop vehicles over a long period of time then there is a smaller deceleration. The smaller the deceleration the less the resultant force and so the less we are affected.
What features do cars have to protect us in car crashes?
Cars have: crumple zones, airbags and seat belts.
How do crumple zones, airbags and seat belts protect us in car crashes?
Crumples zones, airbags and seat belts increase the impact time of a collision. This reduces the rate of change in the momentum and this reduces the impact force experienced.
