Physics - forces and motion Flashcards
Investigating motion
Set up a ramp and a runway, place light gates on the runway, mark out the light gates and make sure distance is the same every time when the experiment is run.
Mark out a line on the ramp (starting point for the car) to make sure the starting point for car is the same every time
Let go of the car and every time the car passes through each light gate, a beam of light is broken and the time it passed is logged. Light gates are useful as you won’t get any timing errors that may arise from human error.
Repeat experiment 3-5 times to get an average time for car to pass each light gate
You can calculate the speed by finding the time it took for the car to pass from the first light gate to the second light gate and the distance between the two light gates
How you can test different things with the experiment on motion
- To investigate gravity and its acceleration on objects, let go of car higher up the ramp
- To investigate mass, modify the car you use (eg a car with more mass) or add weights onto car
- To investigate how friction affects motion, use a different material on the ramp that may cause more friction but keep surface flat to ensure the angle of the ramp isn’t changed
- Changing angle of ramp
Laws of motion (3laws)
First law: Balanced forces mean no change in velocity, when eg drag and thrust of a vehicle are equal, there is no acceleration and it is moving at constant velocity
Second law: If one force is bigger than the other or there is an unbalanced force, there will be a resultant force - F=ma. If there is a resultant force the object will accelerate
Third law: If object A were to exert a force on object B, object B will also exert an equal opposite force onto object A
Force is always equal, but mass and acceleration can be different, eg if object A has a mass of 50 kg, but object B has a mass of 65 kg, object A will have a higher acceleration compared to object B
Investigating Hooke’s law
Using a clamp, clamp a metal spring to a stand
Measure the initial height or length of the spring make sure they are the same and controlled
Measure the masses, make sure they are the same and controlled
below the spring, for each weight you add let the spring extend (come to rest) and measure the new length with an accurate mm ruler (use set square to ensure ruler is straight). Add more and more weights and repeat the process until you have at least 6 measurements
Repeat the experiment 3 times to find an average
Plot results on graph
Instead of a metal spring you can use other elastic material such as a rubber band or metal wire
What effects thinking distance
What effects thinking distance: how fast you’re going. Reaction time: Inexperience, old age, drugs, alcohol, disabilities, visibility,
What effects breaking distance
What effects breaking distance: faulty brakes, mass of the car (more mass means longer it takes to stop), car grip (slippery road, steep road, weather conditions, tyres), speed at which you were going
How momentum is dealt with in cars
In car crashes, a large change in momentum will result in an even larger force on the driver and car. Therefore measures are taken in order to increase the time for the momentum change and therefore to reduce the force. Crumple zones (crumple on impact) are used to increase the time for the car to stop, reducing the force on car Seatbelts stretch and increase the time for wearer to stop, reducing the force acting on the chest Airbags also increase the time of impact to reduce the force and the momentum change
What forces are there
Friction or drag (air resistance)
Normal contact force (acts perpendicular to the surface)
Thrust (push or pull due to an engine or rocket
Electrostatic (between two electrically charged objects
Weight (gravity)
Tension ( in a rope or cable)
Life (due to an aeroplane wing)
How do you reduce drag or friction
- Friction opposes motion: to reduce friction on two objects use a lubricant such as oil
- to reduce drag (in fluids and gases eg. air) : streamline object by using deflectors (lorries and caravans)
Terminal velocity
When acceleration increases, drag or resistance will also start increasing, it will increase to a point where the acceleration equals the drag or resistance and at this point it will have reached terminal velocity where there is zero acceleration
The accelerating force on falling objects is gravity, if there wasn’t air resistance everything will fall at same rate, eg on the moon everything falls at the same rate, gravity works independently meaning mass does not effect it
For a falling object, Air resistance depends on the area and shape
Parachutes increase the air resistance overall
Hooke’s law
The extension is proportional to the force
Length of an unstretched metal wire is called its natural length
If a metal wire is supported at the op and then a weight attached to the bottom, it stretches. The weight pulls down with force, producing an equal and opposite force at the support
A metal spring (or other object) will also obey Hooke’s law if a pair of opposite forces are applied to each end)
How does momentum work
Momentum = mass x velocity P=mv
Momentum is a vector quantity (both magnitude and direction)
Momentum is conserved
Total momentum before = total momentum after
