p2.2-Newtons Laws

Question 1

p2.2.1-How do forces arise(Newtons Third Law)?

Answer 1

The gravitational interaction between a person and the earth produces the same magnitude force. Pairs of forces arise when objects interact. In an interaction pair, each force acts on a different object. The forces are gravitational, the same size and the forces act in different directions.

Question 2

p2.2.1-What are contact forces?

Answer 2

Contact forces are solid surfaces that can exert a force on objects that exert a force on them. Examples of contact forces are friction on a sliding box, drag on a falling leaf, normal contact force on an elephant, up thrust on a floating boat and tension in cord of a bungee jumper.

Question 3

p2.2.1-What are non contact forces?

Answer 3

Some objects interact without being in contact with each other. These forces arise because charges, magnets and masses interact at a distance. Electric charges and magnets both repel and attract, but gravity only attracts. Examples are electrostatics, magnetism and gravity.

Question 4

p2.2.2-What is a free body diagram and how do you draw it?

Answer 4

A free body diagram shows the forces acting on a single object.
1)Identify non-contact and contact pairs
2)Draw the object with arrow showing all the forces acting on the object

Question 5

p2.2.2-How do you calculate resultant forces?

Answer 5

Draw the diagram showing the forces in a triangle. Use pythagorus theorem to work out the hypotenuse.

Question 6

p2.2.3-What is Newton’s first law?

Answer 6

An object will continue to stay at rest or move with uniform velocity unless a force acts on it. It takes a resultant force to change the speed of direction of an object. If the resultant force is 0, the speed or direction won’t change. It’s based on inertia which is a measure of how difficult is to change its velocity. Moving objects keep moving and stationary don’t move.

Question 7

p2.2.3-What is equilibrium?

Answer 7

An equilibrium is a state in which opposing forces or influences are balanced. It is the condition of a system when neither its state of motion nor internal energy state tends to change with time.

Question 8

p2.2.4-What happens when the resultant force isn’t zero?

Answer 8

A resultant force can change the speed of an object and change the direction of motion of an object. If the forces acting on the object aren’t balanced, there is a resultant force meaning the object is either accelerating or decelerating.

Question 9

p2.2.4-How do you calculate with Newton’s second law?

Answer 9

Newton’s second law states that the acceleration that the resultant force produces on the object depends on the size of the resultant force and mass of the object.

force(N) = mass(kg) x acceleration(m/s^2)

Question 10

p2.2.4-How do you experiment with force, mass and acceleration?

Answer 10

Put four masses at the end of the string and use light gates to measure the acceleration. Remove two masses from the end of the string, fix them on top of the trolley and use light gates to measure new acceleration.

Question 11

p2.2.5-How do you explain the motion of falling objects?

Answer 11

When you jump out of a plane, you accelerate and your motion changes because there’s a resultant force on you. As you accelerate, the force of the air increases until the force of air on you is the same as force of earth. Your motion no longer changes as you’ve reached terminal velocity. A parachute increases the force of the air to reduce your velocity.

Question 12

p2.2.5-How do you explain the motion of objects when the forces are at an angle?

Answer 12

Sometimes forces acting on an object aren’t in a straight line. You can analyse these situations by resolving the forces so you’re only dealing with forces that act in two directions at right angles.

Question 13

p2.2.6-What is momentum?

Answer 13

Momentum is the quantity of motion depending on the mass and velocity. Momentum is a vector meaning it takes account of direction. Momentum is conserved meaning it is a constant which is neither created nor destroyed.

Momentum(kg m/s) = mass(kg) x velocity(m/s)

Question 14

p2.2.6-What happens when objects collide and join together?

Answer 14

In an elastic collision, no energy is transferred to other stores. The energy in the kinetic store stays the same. In an inelastic collision, some energy is transferred to other stores.

Question 15

p2.2.6-How do you experiment for conservation of momentum?

Answer 15

1)Set up two air track vehicles on an air track
2)Set up light gates to measure the speed of each vehicle
3)Confirm that if you collide one vehicle moving at a certain speed with a second stationary vehicle, then the second vehicle moves with the same velocity as the first
4)Put plasticine on a stationary vehicle and repeat the experiment. You can find the mass of the plasticine if you know the velocity of vehicle and mass of trolley. Weigh the plasticine to check

Question 16

p2.2.7-What is work and power?

Answer 16

Work is the energy needed to apply a force to move an object in a particular distance. Power is the rate at which work is done.

Power(W) = work done(J) / time(s)

Question 17

p2.2.7-How do you experiment for power of a motor?

Answer 17

You set up a motor with a piece of string with a mass attached. Put the mass on the floor and time how long it takes the motor to lift the mass a certain distance. Calculate work done and power and compare power you have with value of power given for motor.